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2021 Fall Meeting

Functional materials


Integration of advanced materials on silicon: from classical to neuromorphic and quantum applications

The symposium aims at gathering scientists working on monolithic and heterogeneous integrations of new materials, to enable additional functionalities on silicon-based platforms. It considers both classical approaches and emerging topics linked to neuromorphic and quantum applications. The various research fields covered in the symposium pave the way towards highly functionalized Sibased technologies which address current and future challenges in our society.


The microelectronics industry has delivered faster and more efficient computing devices at a remarkably consistent pace for several decades. More recently, the demand for high performance devices and mass data transfer has soared. Driven by new societal needs, linked to the “Internet-ofthings” and the growing demand for ultra-fast data transfer, cognitive systems and new computing paradigms, such as neuromorphic and quantum information processing, have been developed.

Industrials are therefore looking beyond classic architectures and concepts to secure future generations of devices that can be integrated with conventional silicon chip platform. Neuromorphic networks for example require dense arrays of interconnected devices, patterned on silicon using the processing know how generated by the conventional industry. For quantum information science, silicon is also emerging as a promising route. Even for emerging materials that are not yet widely used in the industry, like topological insulators, quantum-dots structures, magnetic or superconductor materials, silicon could be a platform of choice for device integration.

The symposium aims at highlighting novel and innovative approaches that allow for monolithic and heterogeneous integration on silicon technology, application-specific integrated solutions (based on integrated photonics, neural networks, spintronic devices...) or quantum systems. The scope includes the fundamental understanding of new material properties, the implementation of novel integration schemes, the modelling techniques and new application fields. The focus will be on the fabrication, characterization and simulation of materials considered as non-standard for Si technology. Contributions related to innovative hetero-integration techniques will be encouraged. Finally, a particular attention will be given to devices and applications beyond current computation technologies that aim at addressing new computing paradigms such as quantum and neuromorphic computation.

Hot topics to be covered by the symposium:

Material growth, characterization and simulation

Group IV and compound semiconductors:
Group IV materials and alloys (SiGe, GeSn SiGeSn), III-V and II-VI compound semiconductors, grown or transferred on monocrystalline substrates or insulators. Group IV and III-V quantum dots and nanowires integrated on Si.

Oxides and nitrides:
Functional perovskites, ZnO, GaN and heterostructures, oxides with resistive or metal insulator transition, topological insulators, piezoelectric materials, materials for the implementation of neuromorphic devices.

Two dimensional materials:
Growth and transfer of Graphene, Transition Metal Dichalcogenides and Boron Nitride on semiconductors, hybrid 2D/semiconductor devices.

Novel materials for Quantum applications:
Semiconductor/Superconductor Interfaces, Topological insulators, Semiconductor Quantum Dot qubit materials, purified 28 Si, Spin qubit, Si/SiGe Heterostructures.

Integration Techniques

Advanced heteroepitaxy:
Selective growth on patterned substrates, epitaxial lateral overgrowth, self-assembly techniques, remote epitaxy.

Layer Transfer:
2.5D & 3D integration (monolithic & heterogeneous) Innovative synthesis & integration methods of materials and devices used for quantum systems


Data processing and communication:
Advanced CMOS scaling, single electron & single photon devices, neuromorphicarchitectures, IOT, spintronics, ultra-low power & RF e lectronics, Integrated photonics, IR and THz lasers.

Neuromorphic systems:
Bioinspired nano electronics or photonics, neural networks on chips, with possible use in artificial intelligence and machine learning.

Quantum information science and emerging applications of quantum materials:
Quantum communication, quantum computing, quantum sensing.

Life-Sciences application and environmental sensors:
Semiconductor plasmonics, mid-infrared and THz sensing, gas sensors, integration with piezo-materials for MEMS-like sensors and opto-mechanics.

Invited Speakers:

  • Nikolay Abrosimov - IKZ Berlin
  • Gina Adam - Washington University
  • Michael S. Arnold - University of Wisconsin-Madison
  • Alberta Bonanni - Johannes Kepler University Linz
  • Nadine Collaert – IMEC
  • Kimberly Dick – Lund University
  • Inga Fischer - Brandeburg University of Technology Cottbus
  • Anna Fontcuberta i Morral – EPFL
  • Jan Grahn - Chalmers University of Technology
  • José Menéndez - Arizona State University
  • Oussama Moutanabbir - Polytechnique Montréal
  • Nobuya Nakazaki - Sony
  • Kim Sanghyeon - Korea Institute of Science and Technology

Scientific Committee:

  • Abderraouf Boucherif - Université de Sherbrooke
  • Antonio Di Bartolomeo - University of Salerno
  • Giordano Scappucci - TU Delft
  • Jonatan Slotte - Aalto University
  • Farid Medjdoub - IEMN-CNRS
  • Thierry Taliercio - University of Montpellier
  • Douglas Paul - University of Glasgow
  • Luca Pirro - Global Foundries
  • Detlev Grützmacher - Institute for Semiconductor Nanoelectronics
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08:35 Opening Remarks    
III-V and II-VI integration on Si : Chair Giovanni Isella
Authors : Sanghyeon Kim
Affiliations : KAIST

Resume : Recently, monolithic 3D technology has been studied a lot motivated by its various advantages such as reduced footprint and enhanced functionalities of the semiconductor devices. Here, in this talk, we discuss the opportunity of III-V compound semiconductors and group IV materials in monolithic 3D for mixed-signal IC. It will provide a very low thermal budget in top-tier device fabrication, which is very crucial to guarantee the performance of bottom-tier devices. Furthermore, inherent superior physical properties provide improved device characteristics.

Authors : N. Mukhundhan, A. Ajay, J. Bissinger, J. J. Finley, G. Koblmüller
Affiliations : Walter Schottky Institute & Physics Department, Technical University of Munich, Germany

Resume : Solid state systems such as III-V quantum dots (QDs) act as naturally bright and highly efficient quantum emitters that can generate deterministic single or entangled photons pairs. QDs embedded in a nanowire (NW) serve as a platform for site-selective and geometry-controlled in-situ heterogeneous integration onto photonic waveguides (WGs) - a crucial milestone for the realization of an all-integrated quantum photonic circuit (IQPC), with the advantage of scalability for quantum computing and communication. However, systematic studies of the coupling between such a NW based QD emitter and a proximal WG are largely absent. In this work, we use a broadband (0.8 – 1.8 microns) QD emitter with a central wavelength of 1.3 microns, embedded in a GaAs NW that is vertically integrated on a silicon ridge WG, as a model system to explore the physics of light emission, propagation and coupling. We discuss the optimization of geometrical parameters – NW radius and length, WG width and height, and QD axial position – for maximum light extraction efficiency through the WG. We performed broadband FDTD (Finite-Difference Time-Domain) simulations and studied the influence of the parameters on the spontaneous emission enhancement of the QD emitter, and the reflectivities and out-coupling efficiencies at the NW-WG interface, where the fundamental twin HE modes of the NW evanescently couple to the waveguide’s fundamental TE mode. Geometric interferences at the NW-WG interface are observed due to phase differences in evanescent coupling and lead to oscillations in the coupling efficiency and reflectivity over normalized wavelength units. The WG height is found to be the most sensitive parameter for achieving phase matching at the NW-WG interface, with a small variation of 20 nm about the optimum value resulting in a change in peak coupling efficiency of up to 10%. Fabry-Perot resonances are observed in the calculated Purcell enhancement of the dipole emission in the finite NW cavity. These are found to have the dominant influence on the outcoupled power into the WG, with the positions of power coupling peaks closely following the resonances in the Purcell enhancement. We highlight the key considerations for the fabrication of such a device and discuss the parameters that can be tuned to bring the the emission into a peak in power coupling. With an optimized geometry, the peak power coupling achievable for a polarized emission increases to 60% as the QD emitter is positioned closer to the WG (~100nm) inside the NW. This work is supported by the European Research Council (ERC) via the project QUANtIC (ID:771747).

Authors : Preksha Tiwari, Anna Fischer, Pengyan Wen, Svenja Mauthe, Markus Scherrer, Noelia Vico Triviño, Marilyne Sousa, Daniele Caimi, Heinz Schmid, and Kirsten E. Moselund
Affiliations : IBM Research Europe - Zurich

Resume : Si is an abundant material and possesses highly-optimized fabrication processes because it is well-established in the electronics industry. Combined with its low transmission losses in the telecommunication band it is ideal for passive optical structures and thus a promising platform for on—chip photonics and optoelectronics. Due to its indirect band gap however, an alternative material is needed for active devices: III-V semiconductors have a tuneable and direct bandgap, high mobilites and absorption coefficients making them suitable for emitters and detectors covering the entire near-infrared region.[1-4] A challenge needed to be overcome to obtain devices with high material quality though, is the large lattice mismatch between III-Vs and Si. Template-assisted selective epitaxy (TASE) [5,6] offers a way for the local-integration of III-Vs on Si alongside pre-existing structures: Dislocation defects are prevented from propagating, because the III-Vs nucleate at a confined Si seed before filling a predefined hollow oxide template. Here we demonstrate the local integration of 1.5 μm wide and 300 nm thick InGaAs microdisk cavities with evidence of lasing at 300 K in the telecommunication band upon pulsed optical excitation.[7] These cavities have the potential to be scaled further down by introducing metals to the device design.[8] We conceptually show this on optically pumped bonded InP microdisk cavities, where the Au-clad devices benefit from improved heat sinking and show evidence of room temperature lasing down to 300 nm wide cavities, while the InP-only ones do not lase below 500 nm.[9] Besides scaled cavities, emission control is equally important for efficient integrated photonics. We study the influence of Au nanoantennae on bonded InP microdisk cavities and show single mode emission by proper choice of antennae dimensions at room temperature with stable emission down to 200 K while the microdisks without Au antennae are multimode and the dominant resonance wavelength varies with temperature. These results can potentially be extended to monolithically integrated devices with emission in the telecommunication band and give a general insight into advantages of metals for nanolaser architectures. We thank the Binnig and Rohrer Nanotechnology Center (BRNC). This work has received funding from the European Union H2020 ERC Starting Grant project PLASMIC (Grant Agreement #678567), H2020 MSCA IF project DATENE (Grant Agreement #844541). References [1] Kim et al., Nano Letters 17(9), 2017. [2] Baumgartner et al., Opt. Express 29(1), 2021. [3] Tiwari et al., OFC Conference, F2C.2, 2021 . [4] Mauthe et al., Nano Letters, 20(12), 2020. [5] Schmid et al., Appl. Phys. Lett. 106, 2015. [6] Mauthe et al., IEEE JSTQE 25, 2019. [7] Tiwari et al., CLEO Europe, CK4.2, 2021. [8] Nezhad et al., Nature Photon 4, 2010. [9] Tiwari et al., Optics Express 29(3), 2021.

Authors : Korneel Molkens, Ivo Tanghe, Dhruv Saxena, Wai Kit Ng, Riccardo Sapienza, Pieter Geiregat, Dries Van Thourhout
Affiliations : Korneel Molkens - Ghent University, Ivo Tanghe - Ghent University, Dhruv Saxena - Imperial College London, Wai Kit Ng - Imperial College London, Riccardo Sapienza - Imperial College London, Pieter Geiregat - Ghent University, Dries Van Thourhout - Ghent University

Resume : Colloidal quantum dots (CQD) are a very versatile material since they are solution processable and have a tuneable bandgap. They are thus a good candidate for light sources in integrated photonics. Here, we use a silicon nitride on oxide platform, enriched with these CQDs. The CQDs are embedded via spin-coating between two nitride layers to get a high stability and good confinement. Complex waveguide structures can be fabricated from this stack in a very precise way. The CQDs make these waveguides optical active components and thus enable demonstration of various on-chip laser cavities To characterize the precision of the processing, we studied the lasing characteristics of an array of 10 coupled ring resonators. A numerical model suggests that supermodes are formed over all the resonators with distinguishable characteristics. This only happens if the difference in resonant frequency of two resonators due to processing errors is smaller than the splitting in resonant energy due to the coupling. We demonstrate a proof-of-concept of this characterization and show that the resonator energy does not differ more than 5 meV. On the other hand, when disorder is deliberately added to the system, light localization can occur. This is induced by the disorder of the system. The material system we provide here is well suited for the study of this kind of phenomena because of the many geometries that are possible and the temperature stability of CQDs. To conclude, we studied arrays of ring resonators both numerically and experimentally within a silicon nitride CQD platform and studied disorder in this system, both intentional and due to fabrication error.

Authors : Anna Fontcuberta i Morral
Affiliations : Laboratory of Semiconductor Materials, Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland

Resume : Compound semiconductors are at the most suitable material for opto-electronic and solar cell applications. The scarcity of group III elements makes their use in wide consumer applications unviable. Integrating them on silicon in minute amounts as thin films or nanostructure reduces the material utilization up to a factor 1000 and provides the path to integration with silicon electronics. In this presentation we will provide paths for the defect -free integration of III-As compound semiconductors on silicon, involving nucleation of the materials at the nanoscale instead of in the thin film form [1,2]. At the end of the presentation we will explain how this approach can be extended to other families of compounds such as the II-Vs that do not suffer from scarcity on the earth crust [3]. [1] J. Vukajlovic-Plestina et al Nature Comm. 10, 1 (2019) [2] A.M. Raya et al Nanoscale 12, 815 (2020) [3] S. Escobar Steivall et al Nanoscale Advances 3, 326 (2021)

10:30 Q&A session / Break    
Strain relaxation and defects : Chair Monica De Seta
Authors : M. Frauenrath, P. Acosta-Alba, A.-M. Papon, M. Veillerot and J.M. Hartmann
Affiliations : University Grenoble Alpes and CEA-LETI, Grenoble, France

Resume : Nanosecond laser annealing (NLA) might improve the performances of GeSn-on-Ge light emitting devices, through an improvement of their structural quality and a bandgap directness increase (relaxation of the built-in compressive strain). Mainstream annealing processes suffer from Sn surface segregation, as they typically last seconds up to tens of seconds. NLA offers, by contrast, an unique opportunity of annealing GeSn in a highly controlled, non-equilibrium way. NLA experiments were thus performed on tens of nm thick GeSn 6%, 10% and 14% layers grown on Ge-buffered Si substrates in our SCREEN-LASSE tool, with energy densities (ED) ranging from 0.525 Jcm-2 up to 1.6 Jcm-2. The pulse duration was 160 ns and the lasing wavelength 308 nm. In-situ Time Resolved Reflectometry (TRR) measurements were performed by recording the reflected signal of a 638 nm wavelength laser shone on the sample surface during laser annealing. TRR enabled us to determine the melt threshold, which shifted towards lower and lower energy densities as the Sn content increased. At the melt threshold, a street grid-like pattern appeared on the GeSn surface which was similar to the Sn diffusion pattern seen in the literature after much longer annealings. The surface structures were, however, a lot smaller here than with mainstream annealings, without any Sn droplets at the end of tails. For EDs just above the melt threshold, molten islands were observed by Atomic Force Microscopy and the GeSn X-Ray Diffraction (XRD) peak shifted towards higher incidence angles because of Sn redistribution. Molten islands multiplied and started to merge as the ED further increased, resulting in a substantial surface roughening, with Zrange values around 50 nm, then. Close to the melt of the whole GeSn layers, i.e. at ED around 1.0 Jcm-2, the sheet resistance decreased by 38% and the TRR signal was higher after annealing. In that full melt regime, surfaces became smooth once again, with RMS roughness around 1.2 nm, and XRD peaks shifted back towards angles characteristic of higher Sn content layers, with a dependence on the starting Sn content. A Sn content of 6.8% was for instance achieved for the GeSn 14% layer. The crystalline quality of these layers was higher than that of GeSn layers annealed at intermediate EDs. The formation of rather high Sn content layers was not reported before for standard annealing processes and might be unique to ultrafast NLA. When the ED further increased, we assumed that the upper parts of the Ge Strain-Relaxed Buffers underneath melted. This led to a continuous increase of the surface roughness. Lots of small islands were then formed on the surface and the Sn content decreased slowly and continuously, as outlined by the shift of the GeSn XRD peak towards that of the Ge SRB.

Authors : T.J Smart, H. Boschker, W. Braun, A.E.M. Smink, D.Y. Kim, L. Majer, J. Mannhart
Affiliations : Max Planck Institute for Solid State Research, Stuttgart, Germany

Resume : The next generation of transistors and microelectronics demands the synthesis of epitaxial thin film devices composed of elements with vastly different physical properties. Therefore an epitaxy technique is required that is efficient, versatile and able to produce ultra-clean thin films. We present a new and promising epitaxy technique called Thermal Laser Epitaxy (TLE), which combines beneficial aspects from existing physical vapor deposition techniques. At its heart, TLE uses continuous-wave lasers to generate vapors from individual elemental sources. The use of lasers for epitaxial growth provides near arbitrary power densities, a lack of source contamination and an increased efficiency due to the source being directly illuminated by the laser. By depositing thin films on Si substrates, we demonstrate that TLE can be performed with every solid, nonradioactive element within the periodic table. Most of the elements tested have been evaporated from free-standing sources, eliminating the needs for crucibles. In addition, we show that significant deposition is achieved with output laser powers less than 500 W. Due to the compact and technologically simple chamber design available to TLE, deposition can be performed with internal pressures below 10-10 mbar, allowing for the growth of ultra-high purity films.

Authors : Daniele Lanzoni (Corresponding author,, Fabrizio Rovaris, Francesco Montalenti
Affiliations : Università degli Studi di Milano - Bicocca

Resume : Controlling the density of dislocations and their spatial distribution in semiconductor heterostructures is an important ingredient of microelectronics device design. Computer simulations can greatly help to shed light on the complex behavior of such line defects, also in view of the severe challenges posed by high-resolution, time-dependent experimental observations. In bulk systems and in ideal corrugation-free (i.e. perfectly flat) films, the dislocation stress fields can be obtained analytically. If one is interested in non-trivial nanostructures or more complex morphologies, numerical solutions via, e.g., Finite Element Methods (FEM) are needed, increasing the computational demand. Here we present a convenient Machine Learning-based approach which allows one to significantly speed up calculations of both forces and total elastic energies, while maintaining the accurate description of the FEM solution. We decompose both energy and forces for an arbitrary dislocation distribution in one and two body terms which can be obtained by simpler and computationally cheaper evaluations. For an assigned morphology, this permits one to use FEM on a reduced configuration space, exploited to build a training set. We then train on such set an artificial neural network (NN) to approximate dislocation energy functions, which allow for a faster evaluation of both energies and forces acting on a system of an arbitrary number of dislocations. This new approach is here tested in simulations of SiGe films on Si(100), a system of direct interest for the microelectronic industry. Specifically, we focus on the influence of surface undulations on the minimum-energy distribution for dislocations. This is achieved by standard Monte Carlo (MC) implementations where time-consuming FEM energy calculations are replaced by faster and cheaper NN approximations. Results are consistent with previous experimental and theoretical investigations. In particular, the formation of interfacial arrays of edge dislocations has been obtained for flat films, while isolated 60° dislocations are predicted for films with strong undulations. Importantly, the overall computation speed-up obtained using the NN functions exceeded three orders of magnitude. The NN functions have also been exploited to run dislocation dynamics simulations based on the fitted Peach-Koehler forces. Results for graded SiGe layers show the presence of a thermodynamic driving force towards the formation of dislocation pile-ups and are here illustrated. Our method is currently implemented in 2D only. Extensions to full 3D problems, however, are envisioned and could provide a valuable tool to explore large distribution of dislocations in complex geometries.

Authors : Tetzner, H.(1), Fischer, I. A.(2), Skibitzki, O.(1), Mirza, M. M.(3), Manganelli, C. L.(1), Seifert, W.(1), Luongo, L.(1), Spirito, D.(1), Paul, D. J.(3), De Seta, M.(4) & Capellini, G.(1,4).
Affiliations : (1) IHP-Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt(Oder), Germany (2) Experimentalphysik und Funktionale Materialien, BTU Cottbus-Senftenberg, Erich-Weinert-Straße 1, 03046 Cottbus, Germany (3) James Watt School of Engineering, University of Glasgow, Glasgow G12 8LT, United Kingdom (4) Dipartimento di Scienze, Universita Roma Tre, Viale G. Marconi 446, 00146 Roma, Italy

Resume : In the heteroepitaxy of Ge and GeSi layers on Si substrates the lattice mismatch plastic relaxation leads to the formation of misfit and threading dislocations (TDs). These extended defects can negatively influence the electrical properties of optoelectronic devices based on this material system. Previous investigations of the electrical activity of TDs in either n- or p-doped Ge(Si) films were carried out on devices with threading dislocation densities (TDDs) in the range of 10^7 to 10^10 cm-2 including processing-induced defects [1-3]. Here we exploit a recently reported reverse graded buffer technique using a beneficial second interface in SiGe/Ge/Si heterostructures, to tune the TDD from 2×10^7 cm-2 to 3×10^6 cm-2 in intrinsic Si0.04Ge0.96 layers featuring same thickness and plastic relaxation degree [4]. We have conducted a comprehensive analysis of the influence of TDD on the vertical transport mechanisms in as-grown Ge0.96Si0.04/Ge/Si heterostructures without introducing processing-induced defects e.g. by implantation. Temperature dependent current-voltage measurements reveal TDs as source for leakage currents showing a stronger than linear dependency, which indicates electric field dependent transport. Estimated activation energies verify field dependent carrier generation like trap-assisted tunneling as dominant mechanism of transport at room temperature and below. Emission via traps by the Shockley-Read-Hall generation [5] is limited to higher temperatures (>100 °C). [1] E. Simoen, G. Eneman, G. Wang, L. Souriau, R. Loo, M. Caymax, C. Claeys, J. Electrochem. Soc. 157, R1 (2010) [2] C. Claeys, E. Simoen, G. Eneman, K. Ni, A. Hikavyy, R. Loo, S. Gupta, C. Merckling, A. Alian, M. Caymax, ECS J. Solid State Sci. Technol. 5, P3149 (2016) [3] E. Simoen, B. Hsu, G. Eneman, E. Rosseel, R. Loo, H. Arimura, N. Horiguchi, W. Wen, H. Nakashima, C. Claeys, A. Oliveira, P. Agopian, J. Martino, 34th Symposium on Microelectronics Technology and Devices (SBMicro), pp. 1-6 (2019) [4] O. Skibitzki, M.H. Zoellner, F. Rovaris, M.A. Schubert, Y. Yamamoto, L. Persichetti, L. Di Gaspare, M. De Seta, R. Gatti, F. Montalenti, G. Capellini, Phys. Rev. Mat. 4, 103403 (2020) [5] W. Shockley, W.T. Read, Phys. Rev. 87, 835 (1952)

Authors : Luca Barbisan, Anna Marzegalli, Francesco Montalenti
Affiliations : L. Barbisan, F. Montalenti: L-Ness and Department of Material Science, Università degli Studi di Milano-Bicocca, via R. Cozzi 55, I-20125 Milano, Italy; A. Marzegalli: Department of Physics, Politecnico di Milano, via Anzani 42, I-22100 Como, Italy

Resume : Silicon-germanium and pure germanium are appealing for the microelectronic industry because of their full compatibility with silicon technology combined with several attractive properties, including high saturation velocity, high carrier mobility, and adjustable bandgap. Epitaxial deposition of Ge (or SiGe) on Si is unavoidably accompanied, at least for thick enough films, by nucleation of dislocations. Reducing the density of linear defects threading through the film and reaching the free surface, i.e. the typical active device region, is one of the main present goals of the wide industrial and academic community devoted to the integration of different materials on Si. Threading dislocations, indeed, can be detrimental in terms of device performances. A profound understanding of the microscopic mechanisms determining the typical arrays of dislocations can surely help in devising strategies for controlling the evolution of the defects. Molecular Dynamics (MD) is a valid tool that can be used to shed light on dislocation dynamics. Indeed, several works appeared in the Literature, analyzing dislocation gliding in semiconductor thin films [1, 2]. In non-standard conditions, at high enough temperatures and/or in the presence of a sufficient density of point defects, however, dislocations can move also via climbing. At variance with gliding, climbing does not involve the movement of the defect along the typical glide planes. Here we present a set of classical MD simulations, made using the LAMMPS code [3], based on the Tersoff potential [4], aimed at understanding the atomic-scale mechanisms leading to climbing towards the Si/Ge interface of typical dislocations in a Ge/Si(001). To observe climbing we have devised the following original procedure. Straight dislocation are conveniently inserted in a simulation cell including a Ge film over a Si substrate. At a certain rate, individual vacancies are created in the cell and evolved for a certain time at a high-temperature T= 1100K, sufficient to allow for vacancy diffusion to the core of the dislocation. We observe vacancies progressively decorating the dislocation core until a shift of the full core is achieved. Based on the trajectories observed in our MD simulations we can directly observe the influence of the dislocation on the random walk of the vacancies, which are irreversibly attracted towards the core of the defect. Clustering of vacancies both at the core or in its proximity is however observed in some cases, hindering full climbing. The mechanism leading to disgregation and reformation of the core is very clearly observed at the atomic scale, providing new interesting details on a mechanism poorly investigated so far in the literature. [1] A. Marzegalli, Phys Rev B, 88, 165418 (2013). [2] A. Marzegalli, Appl Phys Lett 86, 041912 (2005). [3] S. Plimpton, J Comp Phys, 117, 1-19 (1995). [4] J. Tersoff, Phys Rev B, 39, 5566 (1989). [5] A. Stukowski, Modelling Simul. Mater. Sci. Eng. 18, 015012 (2010).

12:15 Q&A session / Break    
Heterostructures and interfaces : Chair Anna Fontcuberta i Morral
Authors : S. Koelling,1 S. Mukherjee,1 A. Attiaoui,1 P. Del Vecchio,1 G. Fettu,1 M. F. Dumas,1 S. Assali,1 M. Bauer,2 B. Paquelet Wuetz,3 A. Sammak,3 G. Scappucci,3 O. Moutanabbir1
Affiliations : 1 Department of Engineering Physics, École Polytechnique de Montréal, Montréal, Québec, Canada 2 Applied Materials Inc., Sunnyvale, California, United States 3 2QuTech and Kavli Institute of Nanoscience, TU Delft, Delft, Netherlands

Resume : Harnessing quantum processes in semiconductor heterostructures has been a versatile paradigm to engineer a variety of low-dimensional systems to serve the pressing needs for innovative devices for quantum optoelectronics and quantum electronics. Regardless of the material system and the targeted applications, scaling these building blocks requires rigorous, wafer-scale control of the uniformity of the processed devices. Herein, by using group IV semiconductors as model systems we highlight the central role of the atomic-level structure in shaping the optical and electronic properties. Examples from Ge/SiGe, Si/SiGe, and Ge/GeSn quantum wells will be presented and discussed with emphasis on the effects of interfacial broadening and disorder on charger carrier quantum states. Laser-assisted atom probe tomography, combined with a variety of characterization methods and theoretical frameworks, has been exploited to dissect materials and devices on an atom-by-atom basis to achieve 3-D maps of quantum wells and buried interfaces. The properties of the latter are quantified, and their characteristics are extracted shedding new light on the behavior of carrier scattering, spin properties, and carrier confinement in the aforementioned group IV low dimensional systems. Moreover, the role of these atomic-level details in improving theoretical models, designing new materials and devices, and predicting the larger-scale uniformity of quantum devices will also be discussed.

Authors : Tsang-Hsuan Wang1,2, Robert Gehlhaar1, Thierry Conard1, Jan Genoe1,2, Clement Merckling1,3
Affiliations : 1: Imec, Kapeldreef 75, B-3001 Leuven, Belgium 2: ESAT Departement, KU Leuven, Kasteelpark Arenberg 10, B-3001 Leuven, Belgium 3: Department of Materials Engineering (MTM), KU Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium

Resume : Epitaxially grown strontium titanate (SrTiO3, STO) is an essential interlayer that enables the integration of functional perovskite oxides on large scale substrates of Si(001) thus enabling a wide range of applications in electronics and photonics. As a buffer layer, the crystallinity of STO directly impacts the properties of the oxides on top. In this study, we varied the molecular oxygen exposure amount prior to the STO growth to control the SrO/Si interface conditions. We show how the oxygen not only impacts the interface but also the crystallinity and more interestingly the stoichiometry in the STO films. With overexposure of molecular oxygen, the chemical binding states show the formation of SiOx, resulting in amorphous growth of the STO. In addition, the stoichiometry of Sr/(Sr+Ti) ratio changed dramatically as the exposure amount increased. The change of crystal quality and stoichiometry is also reflected in the optical constants, with a reduction nk observed. The change of stoichiometry is linked to the formation energy of different oxides, confirming the importance of controlling the oxygen amount in direct STO epitaxy on Si substrates. Finally, additional annealing shows an improvement by reducing the absorption of the STO films, which is crucial for photonic applications. “This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 864483 and 742299)”.

Authors : Reichmann, F.* (1), Scalise, E. (2), Becker, A. (1), Hofmann, E. V. S.(1)(3)(4), Dabrowski, J. (1), Montalenti, F. (2), Miglio, L.(2), Curson, N. J.(3)(4), Mulazzi, M. (5), Klesse, W. M. (1), Capellini, G.(1)(6)
Affiliations : (1)IHP – Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany; (2)L-NESS and Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 55, I-20125 Milano, Italy; (3)London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, UK; (4)Department of Electronic and Electrical Engineering, University College London, London, WC1E 7JE, UK; (5)Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany; (6)Dipartimento di Scienze, Università Roma Tre, V.le G. Marconi 446, I-00146 Rome, Italy

Resume : A promising approach to improve current GeSn-based photonic and electronic devices is the growth of low-dimensional Sn/Ge(001) structures [1,2], but details on the subsurface electronic structure have remained elusive. Even for the pristine Ge(001) surface, in this regard the simpler system, ambiguities about the room temperature occupation and origin of a surface state above the valence band top exist up to date [3,4]. Angle-resolved photoelectron spectroscopy (ARPES) is a powerful technique that enables direct probing of the k-space-resolved electronic band structure of the occupied states. Accordingly, we combined ARPES and first-principle calculations to investigate the Ge(001) surface electronic structure and the modification upon Sn adsorption. We observe the occupation of a state above the valence band top on the pristine Ge(001) surface, in contrast to previous reports. We utilized temperature-dependent measurements and first-principle calculations to ascribe the observation of this feature to the occupation of the surface conduction band minimum formed by the c(4x2) reconstruction, proving that the Ge(001) surface is metallic. The adsorption of Sn results in a non-dispersive state within the valence band of Ge(001), which we correlate to the interaction of electronic states from a Sn ad-dimer configuration with the surface resonances of the Ge up-dimer, limited by the structural integrity of the Sn ad-dimer configuration. The adsorption of Sn and the concomitant diffusion after annealing into the sub-surface region results in an increase of the heavy hole effective mass. Our results clarify a long standing controversy about the Ge(001) surface states, uncover the modification of valence states by Sn as well as indicating differences in the GeSn subsurface electronic structure compared to bulk. [1] D. Stange et al., ACS Photonics, 5, 4628 (2018): [2] F. Oliveira et al., Applied Physics Letters, 107, 1 (2015): [3] S. D. Kevan, Physical Review B, 32, 2344 (1985): [4] P. E. J. Eriksson et al., Physical Review B, 77, 085406 (2008):

Authors : Heintz, A.*(1,2), Barzaghi, A.(3), Ilahi, B. (1,2,4), Fafard, S. (1,2), Ares, R.(1,2), Isella, G.(3), Boucherif, A. (1,2)
Affiliations : 1 Institut Interdisciplinaire d’Innovation Technologique (3IT), Université de Sherbrooke, 3000 Boulevard Université, Sherbrooke J1K OA5 QC, Canada 2 Laboratoire Nanotechnologies Nanosystèmes (LN2) —CNRS UMI-3463, Institut Interdisciplinaire d’Innovation Technologique (3IT), Université de Sherbrooke, 3000 Boulevard Université, Sherbrooke J1K OA5 QC, Canada 3 L-NESS and Dipartimento di Fisica, Politecnico di Milano, Via Anzani 42, I-22100 Como, Italy 4 Institut Quantique, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke, Québec, Canada J1K 2R1,

Resume : Integration Germanium (Ge), on the well-established Silicon (Si) platform is foreseen as an enabling technological brick to many technologies including LIDAR, solar cells, Lasers…However the growth of Ge on Si substrate still faces challenges to obtain device quality, mainly due to dissimilarities in lattice and thermal expansion constants which leads to defects creation that are detrimental to device performance. For many years researchers have been trying to tackle the problem by different strategies to reduce the TD density. For example, a compliant substrate using a graphene mesoporous Si membrane was demonstrated to accommodate the strain energy during epitaxy [1]. Another effective method includes the three-dimensional (3D) growth of Ge and/or GeSi on patterned Si substrate in which the TDs are eliminated by propagating the TD lines on the patterned sidewalls due to the formation of crystal facets and free surfaces [2]. This work proposes to combine the benefits of the two approaches to reach the ultimate material quality, the idea is to use mesoporous patterned (pillars) Si substrates for the growth of Ge layers to reduce the mismatch and thermal strain accumulated during the growth and cooling process. We report the effect of Si pillars porosity on the structural quality of Ge epilayers grown by Ge K-Cell in a Chemical Beam Epitaxy chamber. Samples were characterized by HRXRD, SEM, Raman spectroscopy and TEM. Our finding paves the way to the fabrication of compliant substrate which would absorb the strain during epitaxy. [1] Boucherif A., Boucherif A., Kolhatkar G., Ruediger A. and Arès R., Graphene-Mesoporous Si Nanocomposite as a Compliant Substrate for Heteroepitaxy, Small, 13, (2017). [2] Falub, C., Von Kaenel, H., Isa, F., Bergamaschini, R., Marzegalli A., Chrastina D., Isella, G., Müller E., Niedermann P. and Miglio L., “Scaling Hetero-Epitaxy from Layers to Three-Dimensional crystals”, Science. 335, 6507,1330-4. (2012).

15:45 Q&A session    
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Doping in III-V and group IV materials : Chair Clement Porret
Authors : Nobuya Nakazaki1, Gianluca Rengo2, Anurag Vohra2, Erik Rosseel2, Clement Porret2, Andriy Hikavyy2, Roger Loo2, Naoto Horiguchi2, Geoffrey Pourtois2
Affiliations : 1. Sony Semiconductor Solutions Corporation; 2. imec

Resume : Highly-doped epitaxially-grown source/drain materials are key elements for the development of the next generations of transistors such as fin and gate-all-around FET, where high active dopant concentrations are required to obtain the best device performance. This in turn requires deep understandings of the defect formation mechanisms causing dopant deactivation. This paper presents a density functional theory (DFT) study on defect formation in P and As co-doped Si (Si:P:As) and B and Ga co-doped SiGe (SiGe:B:Ga). DFT calculation results for the Si:P:As system indicate that As co-doping is expected to help increasing the active P concentration ([P]) by releasing them from the P-vacancy complexes (PxV) at low [As] [N. Nakazaki et al., EMRS 2019 B.IX.3]. In case of SiGe, having a random distribution of Si and Ge atoms, the formation enthalpy (ΔHf) of defects varies with their local surrounding configuration. For this reason, averaged <ΔHf> values are used. Numerical results obtained for the SiGe:B:Ga system show that Ga co-doping does not help to increase the active [B] in strained SiGe. However, in Ge-rich and relaxed SiGe, the <ΔHf> of activated Ga is found to be lower than that of activated B, indicating that Ga doping may be favorable in this context. Both BxV and GaxV are unstable in comparison with substitutional dopants and are not a likely cause for dopant deactivation. Instead, in strained SiGe, Ga exhibits a tendency to form a stable cluster with B.

Authors : Jean-Michel Hartmann, Joel Kanyandekwe
Affiliations : Univ. Grenoble Alpes, F-38000 Grenoble, France. CEA, LETI, Minatec Campus, F-38054 Grenoble, France.

Resume : Our overall aim was to assess the feasibility of the Low Temperature Cyclic Deposition / Etch (CDE) of tensile-Si:P, in order to engineer the Sources and Drains of advanced n-type Field Effect Transistors. We would like to have high amounts of tensile strain and low resistivities in tensile Si:P layers grown at 550°C, with (i) mainstream Si2H6 and PH3 gases for the non-selective deposition of t-Si:P and (ii) HCl and GeH4 for the selective etching of amorphous Si:P versus monocrystalline Si:P (to have selectivity on patterned wafers). We are targeting “substitutional” P contents [P]subst. higher than 5% and electrical resistivities lower than 0.5 In the current study, we have focused on the deposition in such processes, having shown beforehand that, indeed, t-Si:P could be etched at 550°C with HCl and GeH4 if the process conditions were right (Hartmann J.M. and Veillerot M., 2020 Semicond. Sci. Technol. 35 015015). We have at first quantified, at 550°C, 20 Torr and with the reference H2 carrier flow, the impact of the F(PH3)/(2*F(Si2H6)) Mass-Flow Ratio (MFR) on [P]subst., the Si:P layer resistivity and the growth rate. We succeeded, with a MFR of 0.23, in obtaining a [P]subst. of at most 2.0% and a resistivity as low as 0.38 The t-Si:P growth rate was low, however (3.1 nm min.-1 only). The difference between [P]subst. and the ionized P concentration [P ] (1E21 cm-3, to be compared 2.3E20 cm-3 only) was due to the formation of electrically inactive electrically inactive Si3P4, P3V or P4V clusters that increased the built-in tensile strain. We then showed that a reduction of the H2 carrier flow, from its reference value of a few tens of standard liters per minute down to 1/5th of it, then a chamber pressure increase, from 20 Torr up to 90 Torr, enabled us to dramatically increase [P]subst., from 2.0% up to at most 7.9%. 40 Torr was shown to be the best pressure in order to simultaneously have (i) a high substitutional P concentration (6.3%), (ii) a reasonable t-Si:P growth rate (5.5 nm min.-1) and (iii) a low electrical resistivity (0.41 mOhm. cm), without being hampered by a layer uniformity that would be too degraded to be of use in actual devices. Those t-Si:P layers, grown with a MFR of 0.46, were of superior crystalline quality (in X-Ray Diffraction) and smooth (from haze measurements). In the second part of this study, we will use such 40 Torr deposition conditions, together with 90 Torr HCl and GeH4 etches to evaluate, first on blanket Si or SiN-covered wafers, then on patterned Fully Depleted Silicon-On-Insulator substrates with gate stacks, 550°C CDE processes for t-Si:P.

Authors : M. S. Shaikh, Mao Wang, R. Hübner, M. O. Liedke, M. Butterling, D. Solonenko, T. I. Madeira, Zichao Li, Yufang Xie, E. Hirschmann, A. Wagner, D. R. T. Zahn, M. Helm, and Shengqiang Zhou
Affiliations : 1. Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328 Dresden, Germany 2. Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, Bautzner Landstrasse 400, 01328 Dresden, Germany 3. Semiconductor Physics, Chemnitz University of Technology, 09126 Chemnitz, Germany 4. Dresden University of Technology, 01062 Dresden, Germany

Resume : Silicon doped with Tellurium (Te), a deep level impurity, at concentrations higher than the solid solubility limit (hyperdoping) was prepared by ion-implantation and nanosecond pulsed laser melting. The resulting materials exhibit strong sub-bandgap optical absorption showing potential for room-temperature broadband infrared photodetectors [1,2]. As a thermodynamically metastable system, an impairment of the optoelectronic properties in hyperdoped Si materials occurs upon subsequent high-temperature thermal treatment. The substitutional Te atoms that cause the sub-bandgap absorption are removed from the substitutional sites to form Te-related complexes [3,4]. In this work, we explore the phase evolution and the electrical deactivation of Te-hyperdoped Si layers upon furnace annealing through the analysis of optical and microstructural properties as well as positron annihilation lifetime spectroscopy. Particularly, Te-rich clusters are observed in samples thermally annealed at temperature reaching 950 °C and above. Combining the analysis of polarized Raman spectra and transmission electron microscopy, the observed crystalline clusters are suggested to consist of Si2Te3. References: [1] E. Antolin et al. Appl. Phys. Lett. 94, 042115 (2009) [2] J. T. Sullivan et al. IEEE J. Phot. 5, 212 (2015) [3] M. Wang et al. Phys Rev Applied 10,024054 (2018) [4] M. Wang et al. Phys Rev Materials 3,044606 (2019)

Authors : Daniel McDermott1,2, Clement Porret2, Valerie Depauw2, Guillaume Courtois3, Rufi Kurstjens3, Aaron Mac Raighne1, Catherine Grogan1, David O’Brien1, Robert Langer2 and Roger Loo2
Affiliations : 1 Technological University Dublin, Grangegorman Lower, Dublin 7, Ireland 2 Imec, Kapeldreef 75, 3001 Leuven, Belgium 3 Umicore, Watertorenstraat 33, 2250 Olen, Belgium

Resume : Epitaxial growth processes offering high throughputs are essential for industrial applications. Growth rates are limited to ~ 40 nm/min for the heteroepitaxy of blanket Ge/Si virtual substrates (VS) using GeH4 in our hardware setup. GeCl4 is a liquid precursor that can be used for the CVD of high-quality Ge films with enhanced throughput. These films, as grown or transferred to receiver wafers, are required for applications in the fields of photonics, photovoltaics, and logics. This contribution presents an assessment of the capabilities offered by GeCl4. First, the growth kinetics in the 400 to 850°C range, at reduced and atmospheric pressures, on Si and Ge/Si VS were analyzed. Thereby, boundaries were defined between the temperature-limited regime, characterized by an activation energy of about 90 kcal/mol, and the mass transport regime. This allows an optimization of the throughput, with growth rates approaching 200 nm/min. Working with such high growth rates does not significantly impact the morphology of the grown layers. This process is therefore expected to yield highly crystalline materials, as confirmed by XRD. A systematic comparison of the structural properties of the grown materials will be proposed to confirm the materials crystallinity. Preliminary doping studies were also carried out using B2H6 as a dopant source. Attunable doping levels ranging from 1x1017 to 1x1019 cm-3, with full dopant activation, were demonstrated by comparing electrical and SIMS data.

10:15 Q&A session / Break    
Group IV materials for infrared photonics-I : Chair Giovanni Isella
Authors : Inga Anita Fischer
Affiliations : Experimental Physics and Functional Materials, Brandenburg Technical University Cottbus-Senftenberg, 03046 Cottbus

Resume : Refractive index sensing is a highly sensitive and label-free detection method for molecular binding events. Commercial implementations of biosensors based on plasmonic resonances typically require significant external instrumentation such as microscopes and spectrometers. Few concepts exist that are based on direct integration of plasmonic nanostructures with optoelectronic group-IV devices for on-chip integration. Here, we discuss concepts for CMOS-compatible refractive index sensors with a particular focus on how the interaction of plasmonic resonances and photonic modes such as waveguide modes or optical modes in nanostructured photodetectors can be exploited for devices with high sensitivities. We present examples how the interplay of material properties and device geometry can be tailored for applications.

Authors : J. Schlipf1, F. Berkmann2, K. Guguieva2, Y. Kawaguchi2, D. Weißhaupt2, Y. Yamamoto3, J. Schulze2, I. A. Fischer1-3
Affiliations : 1. Chair of Experimental Physics and Functional Materials, BTU Cottbus–Senftenberg, Erich-Weinert-Strasse 1, 03046 Cottbus, Germany 2. Institut für Halbleitertechnik, Universität Stuttgart, Pfaffenwaldring 47 70569 Stuttgart, Germany 3. IHP-Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany

Resume : All-dielectric metasurfaces have been the focus of extensive research in recent years. They can be applied in numerous areas of photonics, enhancing light-matter interaction and providing selectivity for photon energy and polarization. One possible application is their incorporation into Ge photodiodes. Device concepts have already been implemented for fiber communications, where high optical responsivity over a large wavelength range with a relatively thin absorbing layer allows for high bandwidth. However, in spectroscopy, high spectral selectivity is required as well, presenting an additional challenge. Here, we present a feasible design of a metasurface-enhanced vertical Ge photodiode with spectral selectivity for possible spectroscopic applications, fabricated through a simple top-down process in Si-Ge technology. The device is realized on a silicon-on-insulator substrate, enabling excellent confinement of photonic modes in the absorbing Ge layer. We optimized the device geometry numerically for high spectral selectivity. Simulations help understand the interplay of different complex photonic modes and their dependence on geometry. We experimentally demonstrate wavelength-selective absorption enhancement through optical reflection and transmission measurements, de-embedding the effects of the substrate. The resulting absorption spectra show narrow peaks (FWHM < 35 nm) and qualitatively confirm the predictions of the simulations.

Authors : Luciana Di Gaspare, David Stark, Muhammad Mirza, Luca Persichetti, Michele Montanari, Sergej Markmann, Mattias Beck, Thomas Grange, Stefan Birner, Michele Virgilio, Chiara Ciano, Michele Ortolani, Cedric Corley, Giovanni Capellini, Douglas J. Paul, Jérôme Faist, Giacomo Scalari, Monica De Seta
Affiliations : Dipartimento di Scienze, Università Roma Tre, Roma 00146, Italy; Institute for Quantum Electronics, Department of Physics, ETH Zürich, Switzerland; James Watt School of Engineering, University of Glasgow, Glasgow G12 8LT, United Kingdom; Dipartimento di Scienze, Università Roma Tre, Roma 00146, Italy; Dipartimento di Scienze, Università Roma Tre, Roma 00146, Italy; Institute for Quantum Electronics, Department of Physics, ETH Zürich, Switzerland; Institute for Quantum Electronics, Department of Physics, ETH Zürich, Switzerland; nextnano GmbH, Konrad-Zuse-Platz 8, München 81829, Germany; nextnano GmbH, Konrad-Zuse-Platz 8, München 81829, Germany; Dipartimento di Fisica “E. Fermi,” Università di Pisa, Pisa 56127, Italy; Dipartimento di Scienze, Università Roma Tre, Roma 00146, Italy; Sapienza University of Rome, Department of Physics, Piazzale Aldo Moro 2, I-00185 Rome, Italy; IHP - Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, D-15236 Frankfurt (Oder) Germany; IHP - Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, D-15236 Frankfurt (Oder) Germany; James Watt School of Engineering, University of Glasgow, Glasgow G12 8LT, United Kingdom; Institute for Quantum Electronics, Department of Physics, ETH Zürich, Switzerland; Institute for Quantum Electronics, Department of Physics, ETH Zürich, Switzerland;

Resume : The advanced CMOS technology, the available high purity and the high thermal conductivity make Si one of the most attractive substrate for the achievement of low optical loss optoelectronic devices. For silicon photonics a Si-based laser constitutes a long-standing goal, still hindered by the indirect bandgap of group IV materials. An exciting solution is to harness intersubband transitions in quantum cascade structures because such transitions are independent of the bandgap nature. Quantum cascade laser (QCL) has so far only been demonstrated in III-V materials [1]: however, being polar systems, at far infrared energies the QCL is limited to pulsed operation at 250 K with a large electrical dissipation [2]. Developing a QCL based on non-polar group IV materials having weaker electron-phonon interaction is therefore an interesting approach to realize a room-temperature THz QCL [4]. n-type high Ge content Ge/SiGe structures grown on Si(001) are particularly promising. Indeed, the low effective mass, m*=0.13mo, and long non-radiative relaxation times are expected to provide gain values close to those found in III-V QCL at 4 K, and to potentially enable 300 K operation [3]. Here we report on electroluminescence measurements in Ge/Si0.15Ge0.85 quantum cascade emitters on a Si substrate. The strain-compensated 4.2 µm thick multiquantum well (MQW) stack composed by 51 quantum cascade periods was grown on 3.7 micron thick SiGe reverse graded virtual substrate (RGVS) on Ge/Si(001) by UHV chemical vapor deposition. The RGVS has a 97% final Ge content. The MQW stack is embedded between a 400 nm bottom- and a 25 nm top- Phosphorus doped contacts (Nd=2E19 1/cm3). The quantum cascade structure design is based on a single quantum well active region employing a vertical optical transition to unambiguously demonstrate intersubband electroluminescence. The MQW stack was processed into deeply etched diffraction gratings. The devices are characterized at 5 K with an under-vacuum Fourier transform infrared spectrometer. Intersubband electroluminescence at 3.4 and 4.9 THz originating from L-valley transitions in Ge/SiGe MQWs has been demonstrated [4]. The emission spectra are well described by NEGF calculations. The emitters have been benchmarked against a similar GaAs/AlGaAs structure with identical device geometry, finding a Ge/SiGe emission efficiency one order of magnitude lower. This is attributed to a suboptimal injection of the electrons into the upper state of the radiative transitions and to a lower upper state lifetime. The progress on the growth of high quality n-type strain compensated Ge/SiGe quantum cascade structures on Si(001) and the demonstration of intersubband electroluminescence pave the way towards laser action from group IV materials. 1. J. Faist, et al., Science 264, 553 (1994) 2. A. Khalatpour et al., Nature Photonics 15, 16 (2021) 3. T. Grange et al., Appl. Phys. Lett. 114, 111102 (2019) 4. D. Stark et al., Appl. Phys. Lett. 118, 101101 (2021)

Authors : Clement Porret, Srinivasan Ashwyn Srinivasan, Sadhishkumar Balakrishnan, Peter Verheyen, Paola Favia, Patrick Ong, Joris Van Campenhout, Marianna Pantouvaki and Roger Loo
Affiliations : Imec, Kapeldreef 75, 3001 Leuven, Belgium

Resume : CMOS-integrated Si photonics allow to manufacture compact and low power circuits for short-reach optical interconnects. Amongst the required components, Ge-based quantum-confined Stark effect (QCSE) electro absorption modulators (EAM) hold great promises for the realization of broadband optical transmitters operating at > 50 Gbps data rates in the O-band of fiber optic communication, a must for most datacom standards. This work therefore focuses on selective epitaxial growth developments required for the fabrication of such devices integrated in and coupled to a state-of-the-art Si waveguide (WG) photonic platform. A thin n-doped GeSi buffer is first grown and annealed to ensure a full relaxation while minimizing its defectivity. During this step, a specific attention is devoted to controlling material reflow in the WG cavity to ensure a flat buffer surface. Sharply defined and strained-balanced Ge-rich multi quantum well (MQW) layers are then deposited, followed by a p-doped top-contact layer, designed for enabling high speed operations. Systematic cross-sectional inspections performed along these steps demonstrate that managing the facets formed during epitaxial growth is of prime importance for enabling functional devices. The so-fabricated structures exhibit absorption-modulation characteristics in the 1335-1365 nm wavelength range at room temperature with high extinction ratios, demonstrating the potential of this modulator for low-power optical interconnect applications.

Authors : Barzaghi A. (1), Firoozabadi S. (2), Signorelli F. (3), Salvalaglio M. (4,5), Bergamaschini R. (6), Ballabio A. (1), Falcone V. (1), Chejarla V. S. (2), Beyer A. (2), Albani M. (6), Valente J. (7), Voigt A. (4,5), Paul D. J. (7), Miglio L. (6), Montalenti F. (6), Volz K. (2), Tosi A. (3), Isella G. (1)
Affiliations : (1) L-NESS, Dipartimento di Fisica, Politecnico di Milano, Como, 22100, Italy (2) Materials Science Center and Faculty of Physics, Philipps-Universität Marburg, Marburg, 35032, Germany (3) Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan, 20133, Italy (4) Institute of Scientific Computing, Technische Universität Dresden, Dresden, 01062, Germany (5) Dresden Center for Computational Materials Science, Technische Universität Dresden, Dresden, 01062, Germany (6) L-NESS and Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Milano, 20125, Italy (7) James Watt School of Engineering, University of Glasgow, G12 8LT, Glasgow, United Kingdom

Resume : The integration of different semiconductors on silicon is a basic requirement in many fields, such as electronics and photonics. However, the mismatch in lattice parameter and thermal expansion coefficients result in defective epitaxial layers and reduced device performances. A novel approach, named vertical heteroepitaxy (VHE) has been recently demonstrated to address this issue. VHE employs deep patterning of Si wafers to obtain the vertical growth by Low-Energy Plasma-Enhanced CVD (LEPECVD), of a self-assembled array of fully relaxed Ge micro-crystals, featuring the complete expulsion of threading dislocations. Single Photon Avalanche Diodes (SPADs) are one of the most promising approach to single photon detectors, but their performance is limited by the strict requirements in terms of the defectivity of the material employed in their fabrication. Here VHE is exploited to grow self-assembled array of microSPADs, which include the appropriate doping structure required for Geiger-mode operation. Ge is employed as an absorber, to extend the operating wavelength of the device to 1800nm. The crystal morphology has been studied by SEM imaging and the deposition parameters have been optimized to achieve the required crystal shape. The defect density has been found, by both defect etching and TEM imaging, to be lower than in planar epilayers. Finally, the electrical behaviour of single microSPADs has been studied by I-V measurements.

12:30 Q&A session    
Group IV materials for infrared photonics-II : Chair Inga Fischer
Authors : José Menéndez, John Kouvetakis, Chi Xu, D. Ringwala, M. A. Mircovich, C.D. Poweleit
Affiliations : Arizona State University, Department of Physics; Arizona State University, School of Molecular Sciences; Arizona State University, School of Molecular Sciences; Arizona State University, Department of Physics; Arizona State University, Department of Physics.

Resume : GeSn alloys represent the only group IV system with an expected direct band gap over a broad range of compositions. Their electronic structure is similar to that of HgCdTe, featuring a continuum of direct band gaps that reach a value of zero and become "negative" for the end-compound α-Sn. The major difference with the HgCdTe system is the very large lattice mismatch between Ge and α-Sn, which raises questions about the thermodynamic stability of the alloy. Fortunately, this fundamental limitation doesn’t preclude the growth of the material, as several reports on high-Sn alloys have already appeared in the literature. In this presentation I discuss recent optical characterization work on GeSn alloys with Sn concentrations as high as 36%. These materials were synthesized directly on Si substrates using custom CVD methods that combine stannane with polygermanes, making it possible to tune the Sn concentration over a much broader range than previously possible. The measured optical absorption shows that these alloys cover not only the Mid Wave IR (3μm-5 μm), but also the Long-Wave IR (8μm-14 μm) spectral range.

Authors : Luca Persichetti, Michele Montanari, Chiara Ciano, Cedric Corley, Leonetta Baldassarre, Michele Ortolani, Luciana Di Gaspare, Giovanni Capellini, David Stark, Giacomo Scalari, Michele Virgilio, and Monica De Seta
Affiliations : Dipartimento di Scienze, Università degli Studi Roma Tre, Roma, 00146, Italy; Dipartimento di Scienze, Università degli Studi Roma Tre, Roma, 00146, Italy; Dipartimento di Scienze, Università degli Studi Roma Tre, Roma, 00146, Italy; IHP Leibniz-Institut fur Innovative Mikroelektronik, Frankfurt (Oder), 15236, Germany; Dipartimento di Fisica, Università di Roma “Sapienza”, Roma, 00185, Italy; Dipartimento di Fisica, Università di Roma “Sapienza”, Roma, 00185, Italy;Dipartimento di Scienze, Università degli Studi Roma Tre, Roma, 00146, Italy; Dipartimento di Scienze, Università degli Studi Roma Tre, Roma, 00146, Italy and IHP Leibniz-Institut fur Innovative Mikroelektronik, Frankfurt (Oder), 15236, Germany; Department of Physics, ETH Zurich, Zurich, 8093, Switzerland; Department of Physics, ETH Zurich, Zurich, 8093, Switzerland;Dipartimento di Fisica, Università di Pisa, Pisa, 56127, Italy; Dipartimento di Scienze, Università degli Studi Roma Tre, Roma, 00146, Italy.

Resume : The physics of intersubband transitions (ISBTs) in parabolic quantum wells (PQWs) has been recently the subject of intense research, due to the fundamental interest for investigating the strong and ultra-strong light-matter coupling regimes [1] accessible in this quantum system [2], as well as for a plethora of potential device applications like, for instance, THz sources operating at room temperature [3-4]. As a matter of fact, according to the generalized Kohn theorem [5], the energy of ISBTs in PQWs is slightly affected by the density and distribution of electrons in the QW, thus providing a single absorption (and therefore emission) peak at both low and high temperatures. While most of the PQW structures investigated so far have been realized in III–V material systems, CMOS-compatible Ge/SiGe heterostructures are more appealing for industrial applications. Here, we report the structural and optical characterization of a stack of n-doped Ge/Si1-xGex PQWs grown by ultra-high vacuum chemical vapor deposition realizing continuously graded interfaces [6]. The high quality of the samples is confirmed by a thorough structural characterization study that highlights an ideal parabolic compositional profile. By exploring samples with different doping levels (1-6x10^11 cm^-2) and doping geometry, we investigate ISB absorption spectra as a function of temperature, within the range from 10 K up to 300 K. Supported by theoretical calculations, we experimentally demonstrate that in modulation-doped PQWs samples, a single absorption resonance is detected at 4.8 THz, independent of the electron distribution in the subbands and of temperature. The linewidth is ΔE/E is 35% at 300 K, a value comparable to that obtained in III-V at the same temperature. These achievements demonstrate that the improvements made in the epitaxy of Ge-rich SiGe heterostructures on Si substrates make this material platform competitive with respect to the III-V semiconductor one and represent a relevant step forward for the development of CMOS compatible optoelectronic devices in the THz spectral range, where thermal charge fluctuations play a key role. 1. Y. Todorov, A. M. Andrews, R. Colombelli, S. De Liberato,C. Ciuti, P. Klang, G. Strasser, and C. Sirtori, Phys. Rev. Lett.105, 196402 (2010). 2. M. Geiser, F. Castellano, G. Scalari, M. Beck, L. Nevou, and J. Faist, Phys. Rev. Lett. 108, 106402 (2012). 3. C. Deimert, P. Goulain, J.-M. Manceau, W. Pasek, T. Yoon,A. Bousseksou, N. Y. Kim, R. Colombelli, and Z. R. Wasilewski, Phys. Rev. Lett. 125, 097403 (2020). 4. P. Jouy, A. Vasanelli, Y. J. Ulrich, R. Zobl, K. Unterrainer, G. Strasser, E. Gornik, K. D.Maranowski, and A. C. Gossard, Applied Physics Letters 74,3158 (1999). 5. W. Kohn, Phys. Rev. 123, 1242 (1961). 6. M. Montanari, C. Ciano, L. Persichetti, C. Corley, L. Baldassarre, M. Ortolani, L. Di Gaspare, G. Capellini, D. Stark, G. Scalari, M. Virgilio, M. De Seta, Appl. Phys. Lett. 118, 163106 (2021).

Authors : I. Dascalescu 1*, N. C. Zoita 2, A. Slav 1, A.-M. Lepadatu 1, C. Palade 1, D. Buca 3, V. S. Teodorescu 1,4, M. L. Ciurea 1,4, M. Braic 2, and T. Stoica1*
Affiliations : 1National Institute of Materials Physics, 077125 Magurele, Romania; 2National Institute for Research and Development in Optoelectronics, 077125 Magurele, Romania; 3Peter Gruenberg Institute 9 (PGI 9) and JARA-FIT, FZ-Juelich, 52425 Juellich, Germany 3Academy of Romanian Scientists, 54 Splaiul Independentei, 050094 Bucharest, Romania. E-mail*:;

Resume : Crystalline GeSn alloys which at Sn concentration above 6-8at% become direct band gap semiconductors and thus overcome the low efficiency of IR light emission and detection of indirect band gap group IV Si-Ge-C traditional semiconductors. Moreover, the tuning on the band gap with Sn composition leads to the extension of the optical activity of the group IV semiconductors into relevant applications in shortwave infrared (SWIR) of 1.4−3 μm. Cost-effective eco-friendly methods such as magnetron sputtering (MS) deposition of (Si)GeSn alloys are highly desired. We present the synergistic enhancement of the photovoltaic current efficiency by combining in a heterojunction of an epitaxial GeSn layer on Ge buffered Si with a layer of GeSn nanocrystals (NCs) embedded in SiO2. The epitaxial GeSn was deposited on relaxed epitaxial Ge buffer on Si wafer by commonly used RF-MS or by High Power Impulse MS (HiPI-MS). For equivalent growth conditions (deposition rate, sputtering atmosphere and substrate temperature), higher crystalline quality was obtained by HiPI-MS method [1]. The deposition was performed on heated substrates at 200-250oC. The thickness of ~120nm and Sn content of ~12% were evaluated by RBS measurements. The crystallinity was studied by HRTEM, XRD and Raman scattering. The layers of embedded GeSn NCs were obtained by MS co-deposition of Ge, Sn and SiO2 alloys, followed by rapid thermal annealing (RTA) for the formation of GeSn NCs in an inert atmosphere at 400oC [2]. The layer thickness of ~300nm and the concentration of Sn in NCs of 17-18% were measured by TEM and GI-XRD investigation. Spectral photovoltaic current was measured by SWIR illumination though ITO top electrode on diodes constructed either with a single layer of epitaxial GeSn or GeSn NCs, or with a heterojunction stack of p-GeSn-epitaxial/n-GeSn-NCs [1]. The photosensitivity is clearly improved in respect to single epitaxial or NCs layer, by a synergistic effect of combining these layers in a GeSn-epitaxial/GeSn-NCs heterojunction. We acknowledge the support of Romanian Ministry of Research, Innovation and Digitization - UEFISCDI, PN-III-P2-2.1-PED-2019-4468, Core Prgs. NIMP 21N/2019, INOE 33N/2018 and M-ERANET GESNAPHOTO projects. [1] ACS Appl. Mater. Interfaces 12, 56161−56171 (2020) [2] ACS Appl. Nano Mater. 2, 3626−3635 (2019)

Authors : M. Frauenrath, J.M. Hartmann, and E. Nolot
Affiliations : University Grenoble Alpes and CEA-LETI, Grenoble, France

Resume : A light source based on GeSn, a group-IV semiconductor, would minimize energy consumption in electro-optical circuits and enable SWIR and MIR lab-on-chip applications. Electrically pumped lasing, up to 100K, was recently achieved by the University of Arkansas. SiGeSn cladding layers were then used to improve carrier confinement in the GeSn optically active layers. Building upon recent findings on in-situ doped GeSn, we have thus explored the boron and phosphorous doping of SiGeSn. Ge2H6 SnCl4 B2H6 or PH3 chemistries were used for the growth, at 100 Torr and 349°C, of those SiGeSn layers on Ge strain relaxed buffers (SRBs), themselves on Si(001) substrates. X-Ray diffraction (XRD) profiles exhibited well-defined peaks and several thickness fringes, outlining the high crystalline quality of our stacks. The SiGeSn:B XRD peak shifts towards higher incidence angles as the dopant flow increased. This was due to (i) significantly reduced Sn contents or (ii) really high B and/or Si contents. For SiGeSn:P, there was no significant shift of the XRD peak, however. For low and medium B2H6 or PH3 flows, the <110> cross hatch evidenced in Atomic Force Microscopy was less regular than on intrinsic SiGeSn and the surface roughened. RMS roughness and Z ranges were around 2.6 and 20 nm, then, and spinodal decomposition-like surface features appeared. The surface morphology drastically improved for high dopant flows, with a recovering of a regular surface cross-hatch and RMS roughness and Z ranges around 0.4 nm and 3.5 nm, respectively (i.e. values close to that of intrinsic GeSn). A slight increase of the SiGeSn:B growth rate with the dopant flow was otherwise evidenced, while the SiGeSn:P growth rate dropped a bit. Wavelength Dispersive X-Ray Fluorescence (WDXRF) measurements were performed to shed more light on the compositional changes in such quaternaries. Intrinsic GeSn, GeSi and InP calibration samples with known compositions and thickness were used to accurately determine the Si, Sn and P contents in our in-situ doped SiGeSn layers. Most likely because more surface sites were opened, the Si content in SiGeSn:B definitely increased with the B2H6 flow, from 14.5% in i-SiGeSn up to 25% in the most heavily doped sample, while the Sn content dropped a bit, from 9% down to 7%. Higher Si contents would improve electrical confinement in devices, which would be advantageous. Slight Si content decreases and slight Sn increases, from 14% down to 13.5% and from 8.5% up to 9%, were otherwise evidenced in our SiGeSn:P layers as the PH3 flow increased. More P (up to 2.8E20 cm-3 from WDXRF) was otherwise incorporated, for a given Mass Flow Ratio, in SiGeSn than in GeSn. Electrochemical Capacitance Voltage, Secondary Ion Mass Spectroscopy and Transmission Electron Microscopy will be performed in the near future to garner more information about the ion concentration, the atomic concentration and the crystalline structure of our layers.

Authors : O. Steuer1, D. Schwarz2, M. Oehme2, J. Schulze2, M.O. Liedke3, M. Butterling3, A. Wagner3, H. Mączko4, R. Kudrawiec4, I. A. Fischer5, R. Heller1, R. Hübner1, Z. Li1, M. M. Khan1, Y. M. Georgiev1 6, S. Zhou1, M. Helm1, S. Prucnal1
Affiliations : 1 Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany ; 2 University of Stuttgart, Institute of Semiconductor Engineering, 70569 Stuttgart, Germany ; 3 Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany ; 4 Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27,50–370 Wrocław, Poland ; 5 Experimental Physics and Functional Materials, Brandenburgische Technische Universität Cottbus-Senftenberg, 03046 Cottbus, Germany ; 6 Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria ;

Resume : Ge1-xSnx alloys are promising materials for future applications in opto- and nanoelectronics. Alloying Ge with Sn enables effective band gap engineering and Ge1-xSnx alloys exhibit much higher carrier mobility than pure Si or Ge. Importantly, Ge1-xSnx alloys are compatible with CMOS technology. Unfortunately, the equilibrium solid solubility of Sn in Ge is less than 1% and pseudomorphic growth of Ge1-xSnx on Ge causes in-plane compressive strain in the Ge1-xSnx - layer, which degrades the superior properties of the alloys. Therefore, efficient strain engineering is required. In this contribution we present strain and bandgap engineering in the Ge0.89Sn0.11 alloy grown on Ge virtual substrate using post-growth nanosecond (ns) - range pulsed laser melting (PLM). Micro-Raman and X-ray diffraction (XRD) show that after PLM with energy density of 0.5 Jcm-2 the Ge0.89Sn0.11 layer is in-plane tensile strained. Simultaneously, as revealed by Rutherford Backscattering spectrometry (RBS) and cross-section transmission electron microscopy (TEM) investigations, the crystalline quality and Sn-distribution in PLM treated Ge0.89Sn0.11 layer is comparable with that of the as-grown sample. The change of the band structure after PLM is also confirmed by low temperature photoreflectance measurements. Positron annihilation lifetime spectroscopy shows that after PLM the concentration of monovacancy-Sn donor complexes is reduced. These results prove that the ns-range PLM treatment is an effective way for band gab and strain engineering in highly-mismatched alloys. This work was supported by the Bundesministerium für Bildung und Forschung (BMBF) under the project "ForMikro": Group IV heterostructures for high performance nanoelectronic devices (SiGeSn NanoFETs) (Project-ID: 16ES1075). We gratefully acknowledge the HZDR Ion Beam Centre for their support with RBS.

18:00 Q&A session    
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2D materials : Chair Clement Porret
Authors : Thierno Mamoudou Diallo (1)*, Mohammad Reza Aziziyan (1), Roxana Arvinte (1), Tadeas Hanus (1), Jean-Christophe Harmand (2), Gilles Patriarche (2), Charles Renard (2), Simon Fafard (1), Richard Arès (1), Abderraouf Boucherif (1)
Affiliations : (1) Laboratoire Nanotechnologies Nanosystèmes (LN2)-CNRS UMI-3463 Institut Interdisciplinaire d′Innovation Technologique (3IT), Université de Sherbrooke, 3000 Boulevard Université, Sherbrooke, J1K OA5 Québec, Canada. (2) Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies (C2N), 91120 Palaiseau, France * lead presenter

Resume : The monolithic hetero-integration of different materials and development of quantum devices have been of paramount importance to the material research society as the diverse intrinsic electronic and optical properties of dissimilar materials can be conjugated by the physical stacking of such materials. This is, however, heavily bound to the control of misfit strain during heteroepitaxy. Van der Waals epitaxy (VdWE) can enable epitaxial growth of crystalline semiconductors on (2D) materials, while circumventing the lattice matching issue between the epilayer and the underlying 2D materials, thereby extensively reducing defects density (1,2). While remote epitaxy (3,4) offers one of the most intriguing avenues, demonstrations of functional hybrid heterostructures is hardly possible without deep understanding of the nucleation and growth kinetics of 3D crystals on graphene and their mutual interactions. Therefore, studying the nucleation and growth mechanisms, such as how nuclei are formed, how they evolve in nanomaterials and interact with the underlying substrate are but a few of the most interesting current topics in materials science (5). We have demonstrated superiority of high-resolution transmission electron microscopy (HRTEM), a unique vantage point that provides real-space images as well as atomic-resolution information on the nucleation and early stage growth, as a probe for unraveling the dynamic aspects of such atomistic phenomena. Here, we report new dynamic observation on nucleation, growth mechanisms, and interatomic interactions governing VdWE on freestanding single layer graphene (S-SLG). The rigorous interpretations were made from real-time observations of the nucleation and initial growth of germanium (Ge) on S-SLG by using a TEM. The real-time observations allowed strict and meticulous examinations that unfold the nucleation and the initial behavior kinetics. We also report direct experimental demonstration of the Ostwald ripening process, which governs the coarsening of the Ge particles on S-SLG. Our results also shed light to the importance of the graphene cleanliness, which is crucial for the nucleation process. Furthermore, the epitaxial relationship between the Ge crystals and the S-SLG was also investigated. These findings provide invaluable information about remote interatomic interactions observed for the first time in Ge as well as the nucleation and growth processes, from real-time TEM observation, otherwise unattainable by the conventional means and methods. 1. Koma, A. Van der Waals epitaxy-a new epitaxial growth method for a highly lattice-mismatched system. Thin Solid Films 216, 72–76 (1992). 2. Bakti Utama, M. I. et al. Recent developments and future directions in the growth of nanostructures by van der Waals epitaxy. Nanoscale 5, 3570 (2013). 3. Kim, Y. et al. Remote epitaxy through graphene enables two-dimensional material-based layer transfer. Nature 544, 340–343 (2017). 4. Kong, W. et al. Polarity governs atomic interaction through two-dimensional materials. Nat. Mater. 17, 999–1004 (2018). 5. Kim, B. J. et al. Kinetics of individual nucleation events observed in nanoscale vapor-liquid-solid growth. Science (80-. ). 322, 1070–1073 (2008).

Authors : S. Mazzeo (1), F. Migliore (1), S. E. Panasci (2), E. Schiliro’ (2), G. Buscarino (1,2,3), M. Cannas (1), F.M. Gelardi (1), F. Roccaforte (2), F. Giannazzo (2), S. Agnello (1,2,3)
Affiliations : 1) Department of Physics and Chemistry Emilio Segre’, University of Palermo, Via Archirafi 36, Palermo, Italy; 2) Consiglio Nazionale delle Ricerche-Istituto per la Microelettronica e Microsistemi, Strada VIII 5, Catania, Italy; 3) ATEN Center, University of Palermo, Viale delle Scienze Ed.18, Palermo, Italy

Resume : The increasing interest on few layers transition metal dicalcogenides for electronic and photonic applications drives the study for their wide lateral size preparation and stability. We here report an experimental investigation of the effects of thermal treatments in air or in oxygen controlled atmosphere of few layers MoS2. The mechanical and gold assisted Molybdenite exfoliation procedures have been considered with the final transfer to insulating (SiO2, Al2O3) and conducting (Au/Ni) substrates on silicon with accurate investigation to optimize the transfer process. The number of layers explored ranges from monolayer to bulk. MicroRaman (MR) and Microluminescence (MPL) measurements have been used, with 532 nm laser excitation, together with Atomic Force Microscopy (AFM) to morphologically and electronically characterize the samples. In-situ MR and MPL monitoring of induced effects during thermal treatments has been carried out to investigate the occurring structural and electronic changes. Treatments up to about 400°C in steps of 25-50°C of 2 h duration each and pressure up to 2 bar have been done. Preliminary MR measurements enable to identify through bands E12g, A1g different flakes of lateral size of more than 10 um and up to about 100 um with monolayer thickness in the case of Au assisted exfoliation. During the thermal treatments the bulk samples feature a lateral size reduction on increasing the temperature with a tendency to increase the exciton recombination emission at about 1.8 eV and with minor changes in the Raman bands. By contrast, the few layer MoS2 features a quenching of the MPL without relevant modification of the Raman bands. These results suggest that the electronic features of exciton recombination are influenced by the interaction with the substrate with activation of non-radiative processes in the case of few layers MoS2.

Authors : Miriam Galbiati, Luca Persichetti, Paola Gori, Olivia Pulci, Marco Bianchi, Luciana Di Gaspare, Jerry Tersoff, Camilla Coletti, Philip Hofmann, Monica De Seta, Luca Camilli
Affiliations : Miriam Galbiati; Luca Camilli - Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark; Luca Persichetti; Luciana Di Gaspare; Monica De Seta - Department of Science, Roma Tre University, 00146 Rome, Italy; Paola Gori - Department of Engineering, Roma Tre University, 00146 Rome, Italy Olivia Pulci; Luca Camilli - Department of Physics, University of Rome “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma Marco Bianchi; Philip Hofmann - Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark; Jerry Tersoff - IBM Research Division, T.J. Watson Research Center, Yorktown Heights, New York, New York, 10598, USA; Camilla Coletti - Center for Nanotechnology Innovation @NEST, IIT, Pisa 56127, Italy

Resume : Investigating the interfacial properties between graphene and traditional semiconductors is crucial to developing novel electronics. Even though direct growth of high-quality graphene on Si has not been yet achieved, graphene has been grown on Si with a Ge epilayer even on wafer-scale [1]. Consequently, graphene/Ge has received a great deal of attention, especially when graphene is grown on Ge(110) [2–7]. These studies focus mainly on probing the atomic structure of Graphene/Ge(110) interface and notably on the possible reconstructions of Ge surface as shown by scanning tunnelling microscopy (STM). Here, combining STM and angle-resolved photoemission spectroscopy (ARPES) experiments with density functional theory (DFT) simulations, we unveil the interfacial electronic properties of graphene/Ge(110) [8]. In more details, we show that temperature-triggered structural changes at the interface modify graphene’s doping level. After growing graphene by chemical vapor deposition (CVD), the Ge surface results in being passivated by hydrogen that was present in the growth atmosphere [5]. ARPES results show that at this stage graphene is p-doped. The sample is then annealed in vacuum at a temperature above 350 °C. The thermal annealing leads to the desorption of hydrogen and the Ge(110) reconstructs into the (6x2) phase. Here, we find from ARPES data that graphene is interacting more weakly with the Ge substrate, and is now close to doping neutrality. Upon higher-temperature annealing, above 700 °C, the Ge surface modifies further. The Ge surface now shows a symmetry approaching that of the as-grown sample. As discussed in earlier reports, this surface is thought to be stabilized via interaction with graphene [2]. Our ARPES data indeed confirms a stronger interaction in this phase between graphene and Ge, and graphene results now in being n-doped. To gain more insights, we simulate the cases of as-grown and high-temperature annealed samples. Accounting for the presence of acceptor-type defects in Ge [9-10], formed during the CVD process (T> 900 °C), our model successfully predicts the ARPES data. Interestingly, when simulating the sample after high-temperature annealing, we observe that locally some of the topmost Ge atoms rearrange on the surface, as a result of the smaller distance between graphene and Ge, thus creating a certain degree of disorder. The corresponding experimental STM images indeed reveal the presence of such disorder, in addition to many surface defects (most likely vacancies). With this study we have experimentally demonstrated that the electronic properties of the graphene/Ge(110) system are significantly modified by structural changes occurring at the interface. DFT simulations are also used to confirm our hypothesis. Since graphene´s doping level is a parameter of great importance when it comes to graphene devices, the results demonstrate the remarkable flexibility offered by the integration of graphene with CMOS-compatible platforms. References [1] J. Lee, Science, 344(2014). [2] J. Tesch, Carbon, 122(2017). [3] G.P. Campbell, Phys. Rev. Mater., 2(2018). [4] J. Tesch, Nanoscale, 10(2018). [5] D. Zhou, J. Phys. Chem. C., 122(2018). [6] H.W. Kim, J. Phys. Chem. Lett., 9(2018). [7] B. Kiraly, Appl. Phys. Lett., 113(2018). [8] M. Galbiati, J. Phys. Chem. Lett. 12(2021) [9] J. Vanhellemont, Physica B: Condensed Matter, 404(2009). [10] S. Segers, Semicond. Sci. Technol., 29(2014).

Authors : Virginia Falcone (1), Andrea Ballabio (1), Andrea Barzaghi (1), Carlo Zucchetti (1), Luca Anzi (1), Jacopo Frigerio (1), Federico Bottegoni (1), Roman Sordan (1), Paolo Biagioni (2), Giovanni Isella (1)
Affiliations : (1) L-NESS, Department of Physics, Politecnico di Milano, Polo di Como Via Anzani 42, I-22100 Como, Italy (2) Department of Physics, Politecnico di Milano, piazza Leonardo da Vinci 32, I-20133 Milano, Italy

Resume : The epitaxial growth of germanium on silicon enables the microfabrication of Si-based photodetectors with near-infrared (NIR) sensitivity. In this work we report on a new type of detector, obtained from Ge micro-crystals epitaxially grown on a patterned Si substrate. The faceted morphology and relatively high aspect ratio of the micro-crystals was found to enhance the detector responsivity in the wavelength region comprised between the direct (λ≈1550 nm) and indirect gap (λ≈1800 nm) as compared to conventional planar devices. The epitaxial growth was performed by Low-Energy Plasma-Enhanced CVD (LEPECVD). Micro-crystal formation is based on the self-assembly of Ge crystals on a Si substrate, deeply patterned by optical lithography and reactive ion etching. Three-dimensional micro-crystals, several micrometer tall and with a limited lateral expansion are obtained by using optimized growth parameters. Modeling of the near-IR absorption properties of the Ge/Si micro-crystals was done by finite difference time domain simulations (FDTD). The absorptance ratio is always larger than one, with a relevant increase in the indirect gap wavelength range. The main challenge in realizing vertically illuminated photodiodes based on Ge-on-Si micro-crystals is the fabrication of a top transparent contact that can adapt to the 3D-morphology of the sample and bridge the 100-200 nm gap between adjacent microcrystals. Graphene can be used as a suspended continuous top contact, with an absorption that does not exceed 2.4%. After the wet transfer of a single graphene layer, characterization by the scanning electron microscope (SEM) revealed the presence of cracks and discontinuities in the graphene layer placed over the patterned area, generating a “spider web” effect. This was caused by the capillary forces that play an important role for this type of structures in which the distance between the micro-crystals is the order of hundred nanometers. Different strategies were attempted to solve this problem. Eventually, the number of suspended graphene layers was increased and a graphene bilayer was used by modifying the transfer process. The absorption due to the graphene bilayer, was estimated to be ~ 5% which did not significantly affect the efficiency of the optoelectronic device. The fabricated devices were characterized by electrical and optical measurements that confirmed the NIR photoresponse. Responsivity measurements, by a confocal microscope and a supercontinuum laser, proved the enhancement of absorption of this type of structure close to the Ge indirect gap. Fixing the reverse bias Vb = -2V the responsivity of the micro-crystals was almost ten times that of a reference Ge epitaxial layer in the 1650-1800 nm wavelength range. This effect is linked to the light-trapping effects that take place in this structure. Their dependence on the pattern geometry and the micro-crystal morphology, is still under investigation.

Authors : Michael S. Arnold
Affiliations : University of Wisconsin, Madison, WI 53562, U.S.A.

Resume : We have discovered how to drive graphene crystal growth with a large shape anisotropy through control of kinetics on the surface of Ge(001) single crystal wafers and Ge epilayers on Si(001), via CH4 chemical vapor deposition. This discovery enables the direct synthesis of narrow, armchair, semiconducting nanoribbons. The ribbons are self-orienting, self-defining, and have smooth edges. The ribbons exhibit excellent transport properties (e.g., high on-state conductance and on/off ratio at room temperature) and provide a promising pathway towards the direct integration of high-performance nanocarbon electronics onto conventional semiconductor wafer platforms. This presentation will detail the synthesis of these ribbons with widths as narrow as 1.7 nm, the synthesis of seeded nanoribbons and arrays of nanoribbons, the elucidation of their structure, and the characterization of their promising charge transport properties. [1] R. M. Jacobberger, M. S. Arnold, et al., Direct Oriented Growth of Armchair Graphene Nanoribbons on Germanium, NATURE COMMUNICATIONS, 6, 8006 (2015). [2] B. Kiraly, M. S. Arnold, M. C. Hersam, N. P. Guisinger et al., Sub-5 nm, Globally Aligned Graphene Nanoribbons on Ge (001), APPLIED PHYSICS LETTERS, 108, 213101 (2016). [3] R. M. Jacobberger, M. S. Arnold, High Performance Charge Transport in Semiconducting Armchair Graphene Nanoribbons Grown Directly on Germanium. ACS NANO, 11, 8924 (2017). [4] A. J. Way, R. M. Jacobberger, M. S. Arnold, Seed-Initiated Anisotropic Growth of Unidirectional Armchair Graphene Nanoribbon Arrays on Germanium, NANO LETTERS, 18, 898 (2018). [5] M. S. Arnold, R. M. Jacobberger, Oriented Bottom-Up Growth of Armchair Graphene Nanoribbons on Germanium, U.S. PATENT 9,287,359 (2016). [6] M. S. Arnold, A. J. Way, R. M. Jacobberger, Seed-Mediated Growth of Patterned Graphene Nanoribbon Arrays, U.S. PATENT 9,761,669 (2017). [7] A. J. Way, V. Saraswat, R. M. Jacobberger, M. S. Arnold, Rotational self-alignment of graphene seeds for nanoribbon synthesis on Ge (001) via chemical vapor deposition, APL Materials 8 (9), 091104 (2020). [8] V. Saraswat, Y. Yamamoto, H.J. Kim, R.M. Jacobberger, K.R. Jinkins, A.J. Way, N.P. Guisinger, M.S. Arnold Synthesis of armchair graphene nanoribbons on germanium-on-silicon, The Journal of Physical Chemistry C 123 (30), 18445-18454.

16:00 Q&A session / Break    
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Technologies for next generation electronics : Chair Cesar Zota
Authors : Nadine Collaert
Affiliations : imec

Resume : For decades CMOS scaling has been at the heart of technological innovations. With nowadays chip shortages it shows again how semiconductor technology has infiltrated every aspect of our society and daily life: from car industry to customer technology products. With every new generation, CMOS scaling has brought advantages in power, performance, area, and cost. However, with Moore’s law under pressure, a rethinking of what the semiconductor industry calls scaling will be needed. In this talk, we discuss the latest trends in device scaling and show that there is a strong push to technology diversification, blending different technologies together to achieve benefits at the system level. This System-Technology Co-Optimization (STCO) brings the interaction between technology and design to the next level, with 3D technologies taking a central stage. This can go from stacking devices to enabling a functional wafer backside to address the challenges in power delivery and I/O. This system-level optimization does not only benefit logic and memory but also applications in the area of e.g. wireless communication. And next to power, performance, area and cost, we will show that sustainability is becoming one of the important drivers to guide the technology choices.

Authors : Jan Grahn
Affiliations : Chalmers University of Technology

Resume : Quantum computing based on superconducting technology uses single photon signals for processing. These qubits are produced and amplified at microwave frequencies 4-12 GHz typically. The signal power is extremely weak around -145 dBm and must be amplified with highest signal-to-noise ratio at several temperature stages using superconducting and semiconducting low-noise amplification. In this talk, I will describe the most sensitive microwave low-noise amplifier using III-V transistors in the InAlAs-InGaAs heterostructure operating at around 4 K. The design of the material heterostructure, the transistor and the amplifier may all be essential for the final readout of qubits. Some recent work on optimizing the cryogenic low-noise amplifier for operation close to 100 microwatt power dissipation will be presented.

Authors : J. Lespiaux, F. Deprat, B. Rodrigues Goncalves, J. Souc, F. Leverd, M. Juhel, J-G. Mattei, C. Charles, D. Mariolle, and J.M. Hartmann
Affiliations : J. Lespiaux : STMicroelectronics, 38920 Crolles, France ; F. Deprat : STMicroelectronics, 38920 Crolles, France ; B. Rodrigues Goncalves : STMicroelectronics, 38920 Crolles, France ; J. Souc: STMicroelectronics, 38920 Crolles, France ; F. Leverd : STMicroelectronics, 38920 Crolles, France ; M. Juhel : STMicroelectronics, 38920 Crolles, France ; J-G. Mattei : STMicroelectronics, 38920 Crolles, France ; C. Charles : STMicroelectronics, 38920 Crolles, France ; D. Mariolle : Univ. Grenoble Alpes, CEA, LETI, 38000 Grenoble, France ; J.M. Hartmann : Univ. Grenoble Alpes, CEA, LETI, 38000 Grenoble, France ;

Resume : Trench filling with in-situ n-type doped Si faces multiple issues such as growth inhomogeneities along sidewalls or void formation due to a premature closing at the top of trenches (during deposition). Our objective was here to develop a void-free monocrystalline Si:P (c-Si:P) Selective Epitaxial Growth (SEG) process in 1:6 aspect ratio rectangular trenches, in a RP-CVD reactor. A SiH2Cl2 (DCS) + PH3 + HCl chlorinated chemistry was used to reach, at 950°C, 10 Torr, doping levels between 10E17 and 10E18^(-3). Studies were first conducted on blanket wafers: as the HCl flow increased, the Si:P growth rate decreased while the P+ ions concentration was steady. Then, SEG was performed on patterned wafers. A complex recipe with various DCS/HCl mass-flow ratios was needed to fully fill trenches while preventing overgrowth at the trench entrance and voids at the bottom. Then, reliable methods to characterize i) trench filling defects, ii) crystalline quality and iii) phosphorus doping (uniformity and quantification) were evaluated. FIB-SEM 3D, as it enabled to image 3D structures, was most adapted to detect voids in trenches. Meanwhile, cross-sectional TEM images highlighted the excellent crystalline quality of the c-Si:P filling. The P atomic concentration in trenches, from SIMS, was otherwise rather steady as a function of depth, with a value close to the target. This uniformity was confirmed by Scanning Capacity Microscopy.

Authors : Edoardo BREZZA, Fabien DEPRAT, Pascal CHEVALIER, Côme DE BUTTET, Alexis GAUTHIER, Magali GREGOIRE, Denis GUIHEUX, Véronique GUYADER
Affiliations : Edoardo BREZZA: IEMN Lille & STMicroelectronics; all the others: STMicroelectronics

Resume : Advanced heterojunction bipolar transistors needed for high-frequency applications require a precise control of the dopants. The emitter-base junction needs to be finely tuned to achieve good performance. In-situ doped epitaxies used during the fabrication of the device rely on surface preparation to obtain an optimized and repeatable doping profile. The presence of defects due to an imperfect cleaning increases the emitter resistance and low-frequency noise. The base epitaxy is followed by the realization of thin oxide L-shaped spacers and the As-doped emitter epitaxy by Chemical Vapor Deposition (CVD). A cleaning step between spacers formation and emitter epitaxy is mandatory to remove impurities. A highly diluted HF wet cleaning, targeting 5 A of thermal oxide removal, is insufficient for a clean interface, leading to segregation of As, O and F. On the other hand, a too aggressive HF cleaning degrades the spacers HF cleaning and in-situ remote plasma cleaning (Siconi®) processes combined with bake treatments have been tested for the formation of a good emitter-base junction. Siconi targeting 15 A of oxide removal followed by a thermal budget (800 °C, 60 s) in the deposition chamber is the best condition. Low-impurity junction without any As segregation is visible in the doping profile measured by TOF-SIMS. DC measurements validate the advantage of using Siconi®-based cleaning processes, thanks to 50% lower emitter resistance values and reduced dispersion.

10:30 Q&A session / Break    
Quantum technology : Chair Jan Grahn
Authors : N.V. Abrosimov
Affiliations : Leibniz-Institut für Kristallzüchtung (IKZ), Max-Born-Str. 2, 12489 Berlin, Germany

Resume : Isotopically enriched silicon gets more and more scientific and technological interest as a host material for spin qubits [1]. In general, the absence of 29Si atoms showing a nuclear magnetic moment makes 28Si, having no nuclear magnetic moment, very promising for quantum information technologies. Fabrication route of 28Si highly enriched silicon on the way to perfect crystal includes 5 main steps such as production of gaseous silicon tetrafluoride (SiF4) that is used for 28Si enrichment in centrifugal cascades, conversion of 28SiF4 into silane (28SiH4) by the reaction with solid calcium hydride CaH2 followed by rectification process for silane purification, chemical vapour deposition (CVD) of polycrystalline silicon rods by pyrolysis of silane and finally single crystal growth using Floating Zone or pedestal techniques [2]. The main principle for the preparation of pure silicon isotopes is avoiding of any contamination with other isotopes including natural silicon. As result, 4” dislocation free 28Si single crystals with up to 99.9995 at% enrichment and weight of about 5 kg were grown. Two main products of the fabrication route - 28SiH4 and 28Si single crystals - can be used for the production of 28Si epitaxial layers or quantum dots by CVD and MBE techniques, respectively. [1] A. Hollmann, T. Struck, V. Langrock, A. Schmidbauer, F. Schauer, T. Leonhardt, K. Sawano, H. Riemann, N.V. Abrosimov, D. Bougeard, L.R. Schreiber, Phys.Rev.Applied 13, 034068 (2020) [2] N.V. Abrosimov, D.G. Aref’ev, P. Becker, H. Bettin, A.D. Bulanov, M.F. Churbanov, S.V. Filimonov, V.A. Gavva, O.N. Godisov, A.V. Gusev, T.V. Kotereva, D. Nietzold, M. Peters, A.M. Potapov, H.-J. Pohl, A. Pramann, H. Riemann, P.-T. Scheel, R. Stosch, S. Wundrack, S. Zakel, Metrologia 54, 599 (2017)

Authors : Alberta Bonanni
Affiliations : Johannes Kepler University, Linz, Austria

Resume : The tuning of the global band topology by magnetic doping opens wide perspectives for topology driven prospective quantum spintronic technology. An interplay of conservation and breaking of local and global symmetries in topological phases of matter leads to the emergence of topological phenomena including quantum anomalous (QAH) Hall effect, topological superconductivity, and non-Abelian quantum statistics. Magnetically doped topological crystalline insulators (TCI) were foreseen to host topologically protected QAH states generating multiple dissipationless edge and surface conduction channels with Chern number C >1. The symmetry protected topological phase of the SnTe class of TCI, is characterized by a mirror symmetry resulting in topological surface states. Theoretical and experimental studies demonstrated that four Dirac points are located at the time-reversed-invariant-momentum (TRIM) points for the (111) surface of the SnTe compounds. We provide an overview on how we have proven the opening of the gaps at the TRIMs in ferromagnetic Sn1-xMnxTe (111) thin epitaxial layers grown on BaF2(111). The emergence of hysteretic magnetoconductance and anomalous Hall effect point at the onset of a hole mediated ferromagnetic ordering and the anomalous Hall angle is found to be one of the highest recorded for magnetic topological quantum materials [1]. Moreover, we summarize our recent findings on coherent ultra-fast spin dynamics and coupling between magnetism and optical properties in antiferromagnetic epitaxial MnTe [2,3]. References [1] R. Adhikari at al., Phys. Rev. B 100, 134422 (2019). [2] D. Bossini et al., New J. Phys. 22, 083029 (2020). [3] unpublished data

Authors : I. Ahmed(1,2), S. De Gendt(1,2), C. Merckling(1,3)
Affiliations : 1: Imec, Kapeldreef 75, B-3001 Leuven, Belgium 2: Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium 3: Department of Metallurgy and Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium

Resume : With the slowing down of Moore’s law, related to conventional scaling of integrated circuits, alternative technologies will require research effort for pushing the limits of new generations of electronics. Developing topological based qubits is one of the promising methods for realizing fault-tolerant computations within the quantum information technology framework. It is recognized that superconductor/topological insulator heterostructure interfaces may be a perfect host for the exotic “Majorana” particles. These have relevant topological protection nature as required for processing information. Therefore, the physics at the superconductor/topological insulator heterostructure interface need to be studied further, starting at the material level. In this work, a candidate material Barium Bismuthate (BBO) is studied utilizing the Oxide Molecular Beam Epitaxy (MBE) process. The perovskite structure provides opportunity for easily tailored functionality through substitutional doping. Incorporation of potassium into the lattice of BBO results in a superconducting phase with Curie temperature as high as ~ 30K[1]. In addition, BBO is according to DFT based studies, predicted to form topological surface states when doped with Fluorine[2]. In our work, we integrate BBO perovskite on Si(001) substrate, using an epitaxially grown strontium titanate (STO) single-crystalline buffer layer. The volatility of Bismuth requires adsorption-controlled growth to be applied and this is studied within a range of substrate temperatures. Adsorption-controlled growth allows to steer the film stoichiometry even while supplying the volatile element in excess. We designed a set of experiments to better understand the low sticking coefficient issue of Bi atoms to control the stoichiometry in the perovskite films with low defect densities. Determining the single-phase growth window is achieved in-situ with the Reflection High-Energy Electron diffraction (RHEED) system and confirmed ex-situ with the BBO signature peaks within the X-ray Diffraction (XRD) wide range scans, as well as the atomic ratio of Bi/(Bi+Ba) from Rutherford Backscattering Spectrometry (RBS). We do find that the low oxidation efficiency of molecular oxygen is the limiting factor for incorporation of Bi in the perovskite lattice. Activated oxygen plasma is used as an oxidant which reduces the Bi volatility and helps targeting the growth window of the complex oxide. As a conclusion, this work confirms the potential of using activated oxygen plasma as an oxidant source to stabilize pseudocubic epitaxial growth of BBO on the cubic structure STO buffer layer on Si(001) substrate by MBE. Furthermore, understanding of the structural and chemical properties of the heterostructure will be established by utilizing physical characterization techniques such as AFM, and TEM in later stages. This will go hand in hand with the understanding of the ARPES studies and related surface reconstruction of BBO observed by RHEED as a criterion for the high-quality films. “This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 864483)”. References: [1] Yamamoto, H., et al. "Growth of Ba1-xKxBiO3 thin films by molecular beam epitaxy." Physica C: Superconductivity 412 (2004): 192-195. [2] Yan, Binghai, Martin Jansen, and Claudia Felser. "A large-energy-gap oxide topological insulator based on the superconductor BaBiO3." Nature Physics 9.11 (2013): 709-711.

Authors : Yujia Liu1, Carsten Richter1, Thilo Remmele1, Thomas Teubner1, Cedric Corley-Wiciak2, Ketan Anand2, Yuji Yomamoto2, Martin Albrecht1, Nikolay V. Abrosimov1, Giovanni Capellini2,3, Wolfgang M. Klesse2, and Torsten Boeck1
Affiliations : 1 Leibniz-Institut für Kristallzüchtung, Max- Born-Straße 2, 12489 Berlin, Germany 2 IHP – Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt/Oder, Germany 3 Dipartimento di Scienze, Universita degliStudi Roma Tre, Rome, Italy

Resume : A SiGe/Si/SiGe heterostructure is a promising material system for solid-state based quantum computer processors with scalable qubit architecture. The qubits exploit the spins of single electrons, confined in the tensile strained Si. To further enhance the qubit performances, namely to increase the decoherence time T2, we use isotopically enriched 28Si in the active layer to avoid a perturbations of unpaired nuclear spins of 29Si isotopes. Here, we present a 28SiGe/28Si/28SiGe heterostructure on a common Si(001) wafer for qubit application. We have successfully complemented the growth by reduced pressure chemical vapor deposition (RP-CVD) with molecular beam epitaxy (MBE) for the realization of the whole structure. A strain-relaxed buffer (SRB) SiGe layer ca. 5 µm thick is produced on the Si(001) substrate by CVD using conventional Si and Ge precursors. In a second step, isotopically enriched 28SiGe/28Si/28SiGe layers having a whole thickness of around 350 nm are grown by MBE with isotopically enriched 28Si source, where 28Si concentration is more than 99.99%. In this way, we combine the advantage of CVD to produce thick layers at low costs and of MBE to realize thin layers with both high isotopic and elemental purity and structural perfection. This way, the rapid consumption of the MBE sources by wasting the precious material 28Si for purposes other intended can be avoided. Concerning the strain state distribution, the heterostructure was characterized by µ-Raman mapping and scanning X-ray diffraction (XRD). Structural defects have been analyzed by transmission electron microscopy (TEM) both under cross-sectional and plan-view conditions. Secondary-ion mass spectrometry (SIMS) provided valuable insights into the content and distribution of foreign atoms and another isotope 29Si distribution.

12:30 Q&A session / Break    
Materials for neuromorphic devices : Chair Cesar Zota
Authors : Stefania Carapezzi 1, Elisabetta Corti 2, Gabriele Boschetto 1, Siegfried Karg 2, Aida Todri-Sanial 2
Affiliations : 1 Microelectronics Department, LIRMM, University of Montpellier, CNRS, Montpellier, France 2 Department of Science and Technology, IBM Research Europe - Zurich, Ruschlikon, Switzerland

Resume : The development of novel nanomaterials with non-linear properties such as phase change materials or memristive oxides offer new opportunities for energy efficient brain-inspired computing. In this work, we report on a novel and alternative neuromorphic computing paradigm based on oscillating neural networks (ONNs) that are inspired by neural oscillations, and information is encoded in the phase relation of coupled oscillators. In this work, we show results on oscillators based on vanadium dioxide (VO2) to mimic neurons in ONNs. VO2 undergoes a phase transition from a high-resistive monoclinic (M1) crystal structure to a low-resistive tetragonal rutile-like (R) one. This phase transition takes the name of insulator-to-metal transition (IMT), and it is triggered by temperature. The IMT brings a resistive switching in VO2, where the resistivity changes up to several orders of magnitude. It has been observed that resistive switching occurs in VO2 devices, where self-heating is thought to play the central role. We focus on crossbar VO2 devices grown on a silicon platform that have shown to possess advantages compared to the common planar architecture. Even when using beyond-Si technology, the degree of integration with Si technology is important. We use a dedicated technology computer-aided design (TCAD) approach to perform 3D electrothermal simulations of VO2 devices and the associated VO2 oscillator. We report on the thermal aspects that can affect the self-oscillatory behavior of VO2 devices, like 1) VO2 thermal properties and 2) the external temperature. Our findings help shed light on the entangled thermal and electrical behavior of VO2 oscillators and can help provide guidelines for the successful implementation of ONN technology.

Authors : Roberto Guido, Tommaso Stecconi, Youri Popoff, Mattia Halter, Folkert Horst, Antonio La Porta, Roger Dangel, Ute Drechsler, Bert J. Offrein, Valeria Bragaglia
Affiliations : IBM Research-Zurich Säumerstrasse 4 CH?8803 Rüschlikon Switzerland

Resume : Non-Von Neumann architectures with in memory-computing represent a new paradigm for neuromorphic computing. A set of emerging non-linear electrical elements, named memristors, are being extensively investigated for the implementation of dense and power-efficient neuromorphic hardware. In this work we address a class of 2-terminal devices, whose memristive properties originate from redox reactions: filamentary resistive random-access memories (ReRAM). Commonly, the metal-insulator-metal (MIM) stack is realized by sandwiching a transition-metal-oxide (TMO) acting as an oxygen reservoir between an inert and a reactive electrode. In these devices, the conductance depression operation can be performed through analog steps by the application of programming pulses of increasing amplitude; instead, the potentiation operation occurs abruptly through a self-accelerated transition. To target intermediate conductive states during potentiation, a series transistor that complies the maximum current is generally applied. By replacing the commonly used reactive electrode of Ti or TiN with a conductive metal oxide (CMO), such as a sub-stoichiometric TaOx, the device switching polarity reverses and allows for a bidirectional analog conductance update, essential for efficient neural networks training implementations via crossbar arrays. We demonstrate CMOS-compatible TiN/conductive (C)-TaOx/HfO2/TiN memristive devices with exciting characteristics. The CMO material enhances the device performance: a more resistive CMO leads to larger ON/OFF ratios. Thinner CMO films were found to provide superior analog and power consumption performances. In our proposed physical model, resistive switching is controlled by the local, filamentary-bound, O2 incorporation/extraction at the CMO/HfO2 interface. The model is confirmed by replacing the bottom TiN with an inert Pt film: the same polarity and comparable activation energies are found indicating that the switching indeed occurs at the CMO/HfO2 interface. Our work represents a step forward towards the development of scalable and CMOS-compatible neuromorphic synapses, suitable for neural networks training applications.

Authors : Raphael Ahlmann, Stefan Tappertzhofen
Affiliations : Chair for Micro- and Nanoelectronics, Faculty of Electrical Engineering and Informationtechnology, TU Dortmund University, Germany

Resume : Gas sensors are important components for a range of applications. For example, the transition from carbon-based to environmentally friendly mobility essentially relies on hydrogen sensors that allow to detect smallest amounts of gas in case of leakage. In this case, low-cost, low-power, and robust, thin-film gas sensors are required. Here we report on a novel re-configurable sensor type, in which the ambient interacts with the memristive signature of a thin-film oxide. In our previous work we analyzed the nanoionic interactions of ambient oxygen, moisture, and hydrogen with memristive devices. We now suggest exploiting these nanoionic phenomena to develop re-configurable memristive gas sensors. We characterized fundamental electrochemical interactions of ambient gases and the memristive properties and discuss how memristive operation could allow for compensation of degradation and drift effects. Our new sensor concept has the advantage of a nano to almost atomic scale sensing volume, CMOS-friendly integration, ultra-low power consumption, and low-cost mass-fabrication.

Authors : Seongae Park*(1, 2), Stefan Klett(1), Tzvetan Ivanov(1, 2), Andrea Knauer(2), Joachim Doell(2), & Martin Ziegler(1, 2)
Affiliations : (1)Department of Electrical Engineering and Information Technology, TU Ilmenau, Germany; (2)Institute of Micro and Nanotechnologies MacroNano, TU Ilmenau, Germany; * lead presenter

Resume : The development of mobile devices connected to the internet put traditional von Neumann computing paradigms to the challenge of handling mass data. One approach to solving this problem is offered by memristive devices as central building blocks in neuromorphic computing schemes. However, there are a large number of different computational schemes, which impose a wide variety of requirements on memristive devices. In this talk, we present how electrical properties can be tailored for neuromorphic computational schemes using heterogeneous bi-layer TiN/TiOx/HfOx/Au memristive devices as an example. This includes electrical characteristics such as I-V non-linearity, the number of resistance states, electroforming, and the operating voltages, as well as the statistical evaluation of the device variability. For this purpose, the thickness of the HfOx layer and the size of the active device area were varied. In addition, the chemical composition of the HfOx layer was tuned to realize the desired material properties. A 4-inch wafer process was used as the technological platform, which enables a systematic investigation of the physical device parameters across the wafer. Furthermore, the experimental results were supported by numerical simulations. The obtained requirements for the device parameters are discussed regarding the integration into conventional silicon chip platforms.

Authors : Carvalho de Araujo, L. M. *(1), Vilquin, B. (2), Pierron, V. (1), Domengès, B. (3), Wang, Z. (4), Schlom, D. G. (4) & (5), Méchin, L. (1)
Affiliations : (1) Normandie Université, UNICAEN, ENSICAEN, CNRS, GREYC, Caen, France (2) Université de Lyon, Ecole Centrale de Lyon, INL UMR CNRS 5270, Ecully, France (3) Normandie Université, UNICAEN, ENSICAEN, CNRS, CRISMAT, Caen, France (4) Department of Materials Science and Engineering, Cornell University, Ithaca, New York, USA (5) Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York, USA

Resume : Epitaxial La2/3Sr1/3MnO3 (LSMO) shows a ferromagnetic-to-paramagnetic transition at about 360 K that is accompanied by a metal-to-insulator transition above room temperature, which is very promising for uncooled sensors, such as anisotropic magnetoresistances or infrared bolometers [1]. LSMO also presents high sensitivity to strain, hence to mechanical boundary conditions, making it a potential candidate for resonant micro-electromechanical systems (MEMS) [2]. The objective of this work is to investigate the integration of c-oriented AlN on LSMO/SrTiO3/silicon on insulator (SOI). Even though AlN typically exhibits one-tenth the piezoelectric coefficient of Pb(Zr0.52Ti0.48)O3 (PZT) it remains an interesting piezoelectric material since its lower piezoelectric coefficient can be mitigated by a significantly reduced dielectric constant that leads to lower parallel plate capacitance of AlN and an improvement in the signal-to-noise ratio [3]. Due to the larger electro-mechanical coupling that exists between epitaxial films than between polycrystalline films [4], epitaxial integration is expected to allow lower voltage actuation and higher sensitivity detection, through inverse and direct piezoelectric effects. Two deposition methods for AlN thin films were evaluated aiming at a trade-off between material quality and fabrication yield. The AlN films had thicknesses in the 150 – 250 nm range and were deposited at room temperature by sputtering and pulsed-laser deposition (PLD). The LSMO films of thickness in the 20 – 100 nm range were deposited by PLD on SrTiO3-buffered Si or SOI (001) samples deposited by molecular-beam epitaxy. The (00l) orientation of the AlN layers were evaluated by X-ray diffraction, whereas the piezoelectric properties were characterized by piezoresponse force microscopy (PFM). Suspended devices were fabricated using a combination of ion beam etching in argon, reactive ion etching of Si in SF6 gas and etching of SiO2 in HF. The dynamic measurements were performed with a digital holographic microscope (DHM-R2200) and preliminary characterization of the full devices will be presented. [1] V.M. Nascimento et al., J. Phys. D: Appl. Phys. 54 055301 (2021). [2] D.T. Huong Giang et al., Journal of Science: Advanced Materials and Devices, 1, 241 (2016). [3] W. R. Ali, M. Prasada, Sensors and Actuators A 301 (2020) 111756 [4] S. Liu et al., J. Micromech. Microeng. 29 065008 (2019).

Authors : Gina C. Adam
Affiliations : Department of Electrical and Computer Engineering, George Washington University, USA

Resume : Emerging non-volatile memory devices, like resistive switching technology (ReRAM or memristor) have shown potential for the compact and efficient implementation in a variety of applications. However, prototyping a system with these devices is not an easy task given their issues related to manufacturability, reliability and modeling. The nanofabrication and characterization approaches used to optimize the sub-stoichiometric TiO2-x active material and the device design for improved performance and yield at the wafer scale will be presented. Secondly, an approach suitable for modeling of large device populations will be introduced. Lastly, a testing platform will be described which includes a monolithically integrated 20,000 resistive switches / CMOS chip, as well as a custom designed board and software modules for user friendly access. Model / experimental isomorphism across the different layers of abstraction from devices to network, is a guiding principle in this work. These approaches could be easily translated to other novel materials and devices for use in in-memory computing, security primitives or neuromorphic computing.

16:15 Closing Remarks    

Symposium organizers
Cezar ZOTAIBM Research GmbH

Saumerstrasse 4, Ruschlikon, Switzerland

Kapeldreef 75, 3001 Leuven, Belgium
Giovanni ISELLAPolitecnico di Milano

LNESS Dipratimento di Fisica, via Anzani 42, 22100 Como, Italy
Monica DE SETADept. of Science University Roma Tre

Via della Vasca Navale 79, 00146 Roma, Italy