Carrier transport, photonics and sensing in group IV-based and other semiconductors nano devices

Resume : Both deeply scaled down digital microcircuits and gaining an increased importance analog semiconductor systems employ materials different from those in the traditional CMOS electronics. For example, in the emerging IoT and smart automotive applications, sensors receiving analog signals from the physical world and ultra-low power neuromorphic processors include alternative materials. While in the state of the art digital technologies, advanced oxides and compound semiconductors on silicon platforms have been considered, modern analog electronics requires a much wider spectrum of alternative materials. A more complicated device physics of analog devices is superimposed with the need to characterize these materials and their performance after integrating with CMOS. Integration of alternative materials has a lot of challenges for a semiconductor foundry when running diverse analog products and CMOS devices in the same clean room. Segregated areas and strict and complicated contamination protocols are necessary. Additional equipment for characterization, sort and qualification is required. We illustrate how these challenges are addressed on the examples of technologies recently developed and integrated into the CMOS process flows in TowerJazz fabs . The examples include nanosensors based on magnetic tunnel junctions, silicon quasi nanowires and GaN on silicon, memories and 3D capacitors with high-k dielectrics in the back end, RF switches with phase change materials, germanium photodetectors and special nitrides for silicon photonics.

Resume : Ge is one of the candidates to replace Si as a channel material in the next-generation CMOS technology due to the high hole mobility. Furthermore, it is also a promising material for semiconductor spintronics due to its strong spin-orbit interaction (SOI). Until now, the SOI in Ge has been observed in the modulation-doped Ge/GeSi heterostructures, where the hole density can be modulated by applying different voltages on gate metal or by varying the remote doping concentration and the distance between the two-dimensional hole gas (2DHG) and the remote doping layer. In thlis work, we introduce a new ex-situ doping method that can achieve different doping densities in a single undoped Ge/GeSi heterostructure. By implanting Ga with different fluences into the GeSi spacer layer to form a modulation-doped layer, Ge 2DHGs can formed. The carrier density measured at 1.5 K increases linearly with the ion fluence and the carrier activation rate of implanted ions is ~ 40%. Thus, by calibrating the carrier density dependence on the ion fluence, one can modulate the 2DHG density easily. Clear quantum Hall plateau was observed, indicating well sample quality. Acknowledgements This work at NTU has been supported by the Ministry of Science and Technology (106-2112-M-002-009-). This work at Sandia National Laboratories has been supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, US Department of Energy (DOE). This work was performed, in part, at the Center for Integrated Nanotechnologies, a US DOE Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the US Department of Energy’s National Nuclear Security Administration under Contract No.DE-NA-0003525.

Resume : We analyze the size dependence of silicon quantum dots (QDs) electronic band gap. An efficient scheme for the calculation of hybrid and screened hybrid density functionals (DFT) is used to calculate the electronic properties of silicon QDs of size up to ∼800 atoms and volume of up to ∼20nm3. Those calculations are compared with other theoretical estimations and with experimental measurements. We show that the HSE functional yields a band gap that is slightly above the measured optical gap. Finally, we also calculate the ionization potentials of such QDs and show that different approximation methods give similar values.

Resume : The irradiation of bulk silicon with femtosecond infrared pulses is known to result in the production of underdense transient microplasmas. Nonlinear effects associated with the laser beam propagation limits the energy deposition and prevent the material from any permanent modification. Taken together, these two ultrafast laser-semiconductor interaction properties are particularly interesting for controlling and probing silicon-based microelectronic devices by fast, contactless, and noninvasive techniques. In this study, we demonstrate the possibility to generate and transport free-electrons across single isolated Flash memories – and to consequently modify their memory state – with femtosecond laser backside irradiations at 1300 nm wavelength. For both the initially erased and programmed configurations of the device, an identical final state is found after repeated irradiations. This state is interpreted as the one for which the band diagram is flat, as supported by a specifically developed model accounting for two-photon ionization of silicon, quantum tunneling of free-electrons through a 10 nm oxide layer, and recombination of the carriers. Additional experiments performed by varying the laser energy and also by applying a bias on the control gate corroborate this theoretical scenario. The whole set of results holds a lot of promises for fast device analyses (e.g., reliability, defectivity) and for the growing field of ultrafast microelectronics.

Resume : Germanium–tin is probably the most important puzzle for Si photonics due to its direct bandgap nature as the Sn fraction is higher than 8~11% [1]. On the other hand, due to the presence of Sn in the GeSn alloys, strong spin-orbit interaction is expected. For the designs of GeSn-based optoelectronic and spintronic devices, the information of the effective mass is crucial. In this abstract, we present the high-quality modulation-doped Ge0.92Sn0.08/Ge heterostructures grown by reduced pressure chemical vapor deposition. The hole concentration is 3.3 x 10^11 cm^-2 and the mobility is 24,0000 cm^2/V-s at 4 K. Magnetoresistance measurements were also performed at 1.14 ~ 10 K. Well-resolved Shubnikov-de Hass oscillations were observed with clear quantum Hall plateaus. The effective hole mass was extracted to be 0.12 m0. Acknowledgements This work at NTU has been supported by the Ministry of Science and Technology (106-2112-M-002-009-). This work at Sandia National Laboratories has been supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, US Department of Energy (DOE). This work was performed, in part, at the Center for Integrated Nanotechnologies, a US DOE Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the US Department of Energy’s National Nuclear Security Administration under Contract No.DE-NA-0003525. Reference [1] Wirths, S. et al. Lasing in direct-bandgap GeSn alloy grown on Si. Nature Photon. 9, 88–92 (2015).

Resume : Utilizing a thermally induced exchange reaction between single-crystalline Ge nanowires and Al contact pads, we achieved monolithic Al-Ge-Al nanowire heterostructures with atomically sharp interfaces. Integrating such NW heterostructures with various Ge segment lengths as active channels in electrostatically modulated back-gated field-effect transistor devices, we demonstrate the remarkable potential of Al-Ge-Al nanowire heterostructures for nanoelectronic and photonic applications. Devices with short Ge segment length operated at high electric fields show unambiguous signatures of an electrostatically tunable negative differential resistance (NDR) effect in Ge even at room temperature. Modulation of the transfer rates, manifested as a large tunability of the peak-to-valley ratio and the onset of impact ionization is achieved by the combined influences of electrostatic gating, geometric confinement and heterojunction shape on hot electron transfer and by electron-electron scattering rates that can be altered by varying the charge carrier concentration in the nanowire field effect transistors. Thus, the fabricated three-terminal devices could prove to be of great technological interest for operating future devices combining NDR and impact ionization with conventional FET technology. Based on Ge nanowires with diameters comparable to the Bohr radius (aGe = 24.3 nm), we demonstrate quantum ballistic transport in heterostructure devices with ultra-scaled Ge segment lengths of only 15 nm at room temperature. Room temperature operation is a key requirement for the practical application of quantum ballistic transport such as high- performance, low-power dissipating transistors operating at the upper limit of “ON”-state conductance or multivalued logic gates. With respect to photonic applications, photodetectors based on these Al-Ge-Al nanowire heterostructures showed unmatched internal gains exceeding 107 and responsivities as high as 10 A/µW at 532 nm wavelength. This extraordinary high photosensitivity allows for reducing the detector area i.e. the Ge segment length down to sizes at which ballistic transport occurs, thus enabling the first demonstration of an ultrahigh gain quantum ballistic Ge nanowire photodetector also working at room temperature.

Resume : Si nanocrystals (SiNCs) in the quantum size range (2-12 nm) can be made as viable light emitters with emission wavelength that can be tuned from the near-infrared (NIR) into the visible by decreasing their size. Covalent Si-to-carbon bonding offers the possibility of integrating organic dyes for the development of hybrid luminescent materials. H-terminated nanocrystals, produced by thermal disproportionation of silicon oxide, were used as a platform for co-passivation with dodecene and different organic chromophores, e.g. pyrene,[1] porphyrin,[2] or benzothiadiazole chromophores.[3] Excitation of the organic chromophores results in an efficient energy transfer to the nanocrystal core: this is the working principle of a light harvesting antenna. This approach enabled us to circumvent the drawback of the low molar absorption coefficient of SiNCs. The investigated hybrid material exhibits high quantum yield also in the NIR spectral region with lifetime in the µs range. This research has potential applications in bioimaging, taking advantage of time-gated luminescence microscopy to enhance image resolution and in solar energy conversion: we are currently investigating the application of SiNCs in luminescent solar concentrators. [1] J. Phys. Chem. Lett. 2014, 5, 3325; Chem. Mater. 2015, 27, 4390. [2] Faraday Discussion 2015, 185, 481. [3] Chem. 2017, 2, 550.

Resume : Due to its 5d-4f transition, the Cerium ion has an important absorption cross section compare to its other rare earth counterparts. In addition, Ce3+ ion 5d band has an energy levels continuum giving thus wide energy absorption bands for an intense blue emission. Such emission could be applied for Light Emitting Devices (LEDs) generating strong visible blue light with a Si-based matrix compatible with CMOS technology. In the past, a strong Ce3+ ion emission has been detected with a cerium doped SiO2 host matrix. Nevertheless, this system suffers from low rare earth elements solubility as well as the lack of practical material durability after several carrier injections. One of the advantages to use a Si3N4 matrix is the reduction rare earth elements clustering compare to the SiO2. Moreover, such a nitride matrix offers larger electrical carriers injection due to a smaller band gap with respect to the oxide. In order to keep both advantages, a Ce doping SiOxNy matrix is investigated. The aim of this study is to elaborate MOS-LED structure based on Ce3+ doped SiOxNy films. The SiOxNy: Ce3+ layers are deposited on silicon substrates by using RF sputtering technique under N reactive flow. The effect of the matrix composition on carrier injection and transport in fabricated SiOxNy: Ce3+ MOS-LED structures will be investigated and the electroluminescence (EL) properties including I-V characteristic and EL spectra will be analyzed.

Resume : Photoluminescence quantum yield (QY) methodology offers seemingly simple and robust way of assessing the emission efficiency in light emitting materials, such as dyes or semiconductor quantum dots (QDs). Using already standardized and widely used integrating sphere (IS) technique, it has been accepted as the standard methodology even in the industry. Here we show, for the first time, that the very same QY methodology suffers from a critical artifact, independently of the specific implementation, as soon as sample's absorption is compared to a blank reference. This artifact shows as QY dependence on absorption below certain absorption threshold - The lower the absorption, the more are the QY values underestimated. This happens as soon as the uncertainty in the number of measured absorbed photons is approximately 1/10th of the absorption of the sample - e.g. for uncertainty in measured number of absorbed photons of 1%, samples with absorption below 10-15% are already affected and underestimation in QY value is more than 200%. In general, we conclude that every study, where QY of samples with different absorption is compared, is affected, which means that this artifact has been influencing number of published studies (e.g. Nature Nanotechnology 6 (2011) 710, and many others), rendering their conclusions flawed. Using our theoretical simulations, we suggest modified QY methodology with an additional calibration protocol, which needs to be used in every case when QY of samples with varying absorption is evaluated and interpreted.

Resume : In this work, we demonstrate that phonons and photons of different momenta can be confined and interact with each other within the same nanostructure. The interaction between confined phonons and confined photons in silicon resonators arrays is observed by means of Raman spectroscopy. The Raman spectra from large arrays of dielectric silicon resonators exhibited Raman enhancement accompanied with a downshift and broadening. The analysis of the Raman intensity and line shape using finite-difference time-domain simulations and a spatial correlation model demonstrated an interaction between photons confined in the resonators and phonons confined in highly defective regions prompted by the structuring process. It was shown that the Raman enhancement is due to collective lattice resonance inducing field confinement in the resonators, while the spectra downshift and broadening are signatures of the relaxation of the phonon wavevector due to phonon confinement in defective regions located in the surface layer of the Si resonators. We found that, as the resonators increase in height and their shape becomes cylindrical, the amplitude of their coherent oscillation increases and hence their ability to confine the incoming electric field increases.

Resume : Silicon nanowires (NWs) attracts the interest of the scientific community as building blocks for a wide range of future nanoscaled devices. We optimized the synthesis of NWs with a cheap, fast and maskless approach compatible with Si technology by using a chemical etching of Si substrates catalyzed by thin metal layers. NWs realized by this technique exhibit a bright room temperature emission, whose wavelength can be tuned with the NW diameter according to quantum confinement. Low-cost 2D random fractal arrays of vertically aligned Si NWs are obtained by engineering the deposition of fractal Au layers, without any lithography nor masks. The optical response of the system is controlled by the optimization of the NW fractal geometries. Strong in-plane multiple scattering and efficient light trapping overall the visible range are observed due to the fractal structure, remarking the promising potential of Si NWs. These strongly diffusing Si NWs allowed the first experimental observation of a new phenomenon of Raman coherent backscattering, exploiting the role of phase coherence in multiple scattering. Moreover, room temperature bright light emission from Si NWs promoted the realization of light emitting devices, multiwavelength hybrid light sources and of an innovative class of label free optical biosensors, opening the route towards low-cost integrated Si-based photonics and sensing.

Resume : Using Density Functional Theory (DFT), semi-empirical 10 orbital Tight Binding (TB) method and Ensemble Monte Carlo (EMC) simulations we show for the first time that (a) Gunn-Hilsum Effect can be induced in silicon nanowires (SiNWs) with diameters of 3.1 nm under 3 % tensile strain and an electric field of 5000 V/cm, (b) the onset of negative differential resistivity (NDR) in I-V characteristics is reversibly adjustable by strain and (c) strain can modulate the value of resistivity by a factor 2.3 for SiNWs of normal I-V characteristics i.e. those without NDR. Results are explained using electron-phonon scattering mechanisms including both Longitudinal Acoustic (LA) and Optical (LO) phonons involving both inter-sub band and intra-sub band scattering events. It is noteworthy that the observed NDC is different in principle from Esaki-Diode and Resonant Tunneling Diode (RTD) type of negative I-V slopes which originate from tunneling effect. Gunn-Hilsum or Gunn Effect and its associated negative differential resistivity (NDR) emanates from transfer of electrons between two different energy bands in a semiconductor. If applying an electric field transfers electrons from an energy sub band of a low effective mass to a second one with higher effective mass, then the current drops. This manifests itself as a negative slope or NDR in the I-V characteristics of the device which is in essence due to the reduction of electron mobility. In sharp contrast to GaAs, bulk silicon has a very high energy spacing (~1 eV) between sub band minima which renders the initiation of transfer-induced NDR unobservable. However our theoretical observation of Gunn Effect in silicon nanowires are promising for applications in mechanically-tunable microwave oscillators, and electromechanical sensors.

Resume : Silicon nanowires (SiNWs) have been largely studied for application in nanoelectronics, photonics and sensors. In all cases the control of their doping has demonstrated to be crucial as well as difficult. The conventional doping methods, such as ion implantation, can be critical in nanostructures for the difficulty to achieve conformality and abrupt junctions, for the stochastic spatial distribution of the implanted ion and for the severe crystal damage. Other approaches such as the formation of amorphous doped layers over the NWs present the drawback of creating heterointerfaces increasing trapping effects at the junction. An innovative solution to make controlled and conformal doping at nanoscale without bulk or surfacial defects has been recently proposed. This method consists in forming one monolayer of dopant-containing molecules from liquid solutions. Junction depths as small as 5 nm with dopant peak concentrations of 1×1019 cm-3 ca for both p- and n-type doping have been obtained. The method is applied to an array of 1×1010 cm-2 dense SiNWs with 1µm length and diameters up to about 60nm. The optical functionality of the SiNWs array is characterized and it is found that it shows a total reflectance, mainly consisting of the diffuse component, of 10% thus indicating that either the SiNWs strongly absorb the radiation or, alternatively, they have a relevant role in light trapping. The electrical characteristics of SiNWs doped by using the molecular doping are obtained for different junction depths and it is found that the molecular doping method applied to the SiNWs array provides efficient nanostrictured diodes.

Resume : Resonant devices based on photonic crystal microcavities have been proposed and demonstrated in the silicon-on-insulator platform over the last decade. New geometries continue to be developed, which expand the potential domains of application. This presentation will review the evolution of such devices including some that have been demonstrated very recently. Application in biosensing will be discussed.

Resume : Since last decade synthesis and characterization of composite metal oxides nanostructures and finding their new applications has become an active research field. Cadmium Tin Oxide (CTO), cadmium stannate is one of the promising composite oxide system among other composite oxides like ITO, FTO, ZTO, etc. because of its peculiar and interesting optical and electrical properties[1].CTO system usually forms two polymorphs namely as mono and di cadmium stannate CdSnO3 and Cd2SnO4 respectively and both are transparent semiconductor oxides [1,2]. Cd2SnO4 has high carrier charge density in the range of 1018 to 1021 cm-3 and high mobility in the range of 10-100 cm2V-1S-1 and its wide optical band gap make it very promising material for the applications such as a TCO substrate in solar cells [3], photoanode material for solar water splitting system, biodegradation process [3,4]. It has been also explored for Li ion battery and dye sensitized solar cells applications [6]. Interestingly no one has explored the gas sensing properties of Cd2SnO4, while CdSnO3 has shown quite attractive gas sensing properties to various gases such as ethanol, chlorine, ammonia [7,8]. Herein we synthesized pure single phase orthorhombic Cd2SnO4 nanoparticles of cubical morphology by one step solution combustion method using stannous chloride and cadmium nitrate as precursor and citric acid is used as fuel. The structural and morphological properties of the synthesized nanoparticles were investigated using techniques such as X-ray diffraction, and FESEM, TEM. The XRD result of synthesized nanoparticles confirms the pure orthorhombic phase of the particles and morphological study using FESEM and TEM images confirm their uniform growth and cubical shape with edge length around 80 nm. Elemental composition of the synthesized nanoparticles was investigated using Energy-dispersive X-ray spectroscopy measurement. EDX results confirm the synthesized nanoparticles contains Cd and Sn in 2:1 ratio with excess of oxygen without any other impurities. Raman Spectrum obtained at room temperature also investigated of the synthesized nanoparticles. We further investigate the gas sensing properties of the synthesized nanoparticles at three different temperature for the ethanol, acetone, and ammonia gases. Our study suggest that the orthorhombic phase Cd2SnO4 has better sensitivity and response time for ethanol gas than the other gases at all three temperatures. We also suggest the gas sensing mechanism of the synthesized nanoparticles for the ethanol.The gas sensing properties were investigated on the principle of change in resistance of the sensor when exposed to the gas and the change depends on the type and concentration of the gas. The sensitivity of the sensor defined as ΔR/Ra where ΔR is change in resistance of the sensor and Ra is the resistance of the sensor in air. References 1. R.D. Shannon, J.L. Gillson, R.J. Bouchard J.Phys. Chem. Solids, 38, 877-881, (1977). 2. G.Haacke, H. Ando, W.E. Mealmaker J. Electrochem Soc.;SOLID STATE SCIENCE AND TECHNOLOGY, 124, 1923-1926 (1977). 3. Sarika A. Kelkar Energy Environ. Sci., 5, 5681-5685 (2012). 4. Sarika Kelkar, Chinmai Ballal, Aprna Deshpande, Sambhaji Warale, and Satishchandra Ogale, J. Mater.Chem. A, 1, 12426-12431 (2014). 5. Y. Sharma et al. Journal of Power Sources 192, 627–635 (2009). Gayatri Natu , Yiying Wu J. Phys. Chem. C 114, 6802–6807, (2010). 6. S. Dinesh et.al. , Material Science and Engineering B, 214, 37-45, (2016). 7. Chu Xiangfeng, Cheng Zhiming Sensors and Actuators B 98, 215-217, (2004). 8. Arijit De and Susmita Kundu Journal of Materials Engineering and Performance 25, 2746–2751 (2016)

Resume : Silicon nanowires (NWs) are attracting the scientific community for a wide range of application. The realization of a new class of luminescence biosensors based on Si NWs for protein and DNA is demonstrated. These sensors are based on the quenching of the PL signal due to the quantum confinement at room temperature of ultrathin Si NWs. The occurrence of non radiative phenomena introduced by the target analyte on the NW surface determines the quenching of the PL signal. In particular, we realized a sensor for C-reactive protein (CRP), which is crucial for heart-failure pathology. The availability of high sensitivity, low-cost and reliable CRP sensors is a priority demand in clinical diagnosis for cardiovascular diseases. Si NW sensors are fast, highly selective and offer a broad concentration dynamic range. Moreover, these sensors reach a fM sensitivity permitting non-invasive analysis in saliva (1). By changing the functionalization protocol, we realized a label- and PCR-free sensor capable to reveal few copies of Hepatitis B virus without amplification of the DNA and endowed with a strong selectivity. Si NWs open the route towards new optical label-free sensors with low cost and a full industrially compatible approach for the primary health care diagnosis. 1.”New Generation of Ultrasensitive Label-Free Optical Si Nanowire-Based Biosensors”, ACS Photonics, 10.1021/acsphotonics.7b00983, 2017

Resume : The successful light emission from silicon devices is one of the big challenges for optoelectronics and telecommunications, that if won will allow a significant reduction of the costs and fabrication times. Many research groups have investigated for years a way to obtain efficient light emission at 1,5 m from rare earth-doped silicon samples. Unfortunately, Er clustering turned out as a limiting factor in obtaining a sufficient optical gain in Er-doped Si materials. To overcome this issue, we propose a new paradigm for porous silicon structures: moving from Er doping to Er filling. As a matter of fact, looking for an equilibrium between Er content and light emission using 1-2% Er is a dead end road for efficient photoluminescence (PL), given that an insufficient Er content and/or the Er clustering will act as strong limiting factors. In this study, we used a multidisciplinary approach mainly based on needle electron tomography (ET), electrochemistry, EXAFS, PL and electron microscopy. We demonstrate that the pore filling approach leads to enhanced PL emission, with respect to standard Er doping, and that this emission originates from both erbium oxide and silicate. These results then help identifying where to address the efforts towards highly efficient Er-related emission from porous Si. REFERENCES: [1] G. Mula et al. Sci. Rep. 7 (2017), 5957; [2] G. Mula et al. Appl. Surf. Sci. 311, 252–257 (2014); [3] G. Mula et al. J. Phys. Chem. C 116, 11256 (2012).

Resume : An omnidirectional mirror that works for a wide range of light frequencies and all incidence angles is a basic element for infrared communication. In this work, we report a hybrid quantum-classical design of a dielectric multilayer device consisting of an ab initio calculation of the dielectric function for each semiconducting layer with a specific atomic structure [1], followed by a study of wave scattering through the device using the transfer matrix method within the classical electromagnetic theory. The designed omnidirectional mirror consists of stacked multilayer reflectors, each one tuned to a portion of the reflection band. The validation of this design was carried out on a freestanding nanostructured porous silicon multilayer film fabricated by electrochemical etching of a highly-doped p-type [100]-oriented crystalline Si wafer alternating two anodic current densities and finishing with a high current to separate the multilayer from the substrate [2]. The measured infrared transmittance spectra are compared with those predicted from the multiscale design. Finally, we think that multiscale studies based on ab-initio calculations could be a useful alternative for the design of photonic devices. This work has been supported by CONACyT-252943 and UNAM-IN106317. A. P. acknowledges the financial support from PAEP of UNAM. [1] P. Alfaro, A. Palavicini and C. Wang, Thin Solid Films 571, 206 (2014). [2] A. Palavicini and C. Wang, Optics and Photonics Journal 3, 20 (2013).

Resume : CMOS-compatible light emitters are intensely investigated for integrated active silicon photonic circuits. One of the approaches to achieve on-chip light emitters is the epitaxial growth of Ge(Si) QDs on silicon. Their broad emission in 1.3-1.5 um range is attractive for the telecomm applications. We investigate optical properties of Ge(Si) QD multilayers, that are grown in a thin Si slab on a SOI wafer, by steady-state and time-resolved micro-photoluminescence. We identify Auger recombination as the governing mechanism of carrier dynamics in such heterostructures. Then we demonstrate the possibility of light manipulation at the nanoscale by resonant nanostructures investigating Si nanodisks with embedded Ge(Si) QDs. We show that the Mie resonances of the disks govern the enhancement of the photoluminescent signal from the embedded QDs due to a good spatial overlap of the emitter position with the electric field of Mie modes. Furthermore we engineer collective Mie-resonances in a nanodisk trimer resulting in an increased Q-factor and an up to 10-fold enhancement of the luminescent signal due to the excitation of anti-symmetric magnetic and electric dipole modes. Using time-resolved measurements we show that the minima of the radiative lifetime coincide with the positions of the Mie resonances for a large variation of disk sizes confirming the impact of the Purcell effect on QD emission rate. Purcell factors at the different Mie-resonances are determined.

Resume : The search of efficient sources of white artificial illumination has become increasingly widespread in the last years, driving to the development of new hybrid inorganic/organic emitting diodes (WHLEDs) architectures.[1] Following with our research in the design of hybrid luminescent materials,[2] here we report the synthesis of new monochromatic- or the first white-emitting hybrid organometallo-silica nanoparticles. These latter have been prepared using a new synthetic approach consisting of the generation of a central nanobundle, built from the condensation of three different emitting complexes ([Ir(dfppy)2(PPETS)2]OTf, [Ir(ppy)2(PPETS)2]PF6, [Ir(ppy)2(dasipy)]OTf), previous to the formation of the mesoporous silica shield. These emitting nanoparticles have been implemented into a rubber-like coating and tested on top of a UV-LED, providing HLEDs with a very efficient white emission, which is stable over thousands of hours and mimics quite well the visible part of the sunlight spectrum. 1. L. Niklaus, S. Tansaz, H. Dakhil, K. T. Weber, M. Pröschel, M. Lang M. Kostrzewa, P. B. Coto, R. Detsch, U. Sonnewald, A. Wierschem, A. R. Boccaccini and R. D. Costa, Adv. Funct. Mater. 2017, 27, 1601792. 2. C. Ezquerro, A. E. Sepulveda, A. Grau-Atienza, E. Serrano, E. Lalinde, J. R. Berenguer, J. Garcia-Martinez, J. Mater. Chem. C 2017, 5, 9721

Resume : The construction of a semiconductor heterojunction has attracted a lot of attention due to its perfect effectiveness in improving the sensing, luminescence and photocatalytic activity of a wide range of nanomaterials. [1-3] In particular, hybrid nanostructures composed of semiconductor (SC) and metallic nanoparticles (MNP) have received growing interest due to the high confinement associated to the plasmonic resonances of MNP. This phenomenon enables strong interactions with other photonic elements such as quantum emitters. [4] The resulting plasmon-exciton interaction gave benefits to a wide range of applications such as gas and vapor sensing, hydrogen storage, electro-optics, and catalysis. In this context, we develop a metal-semiconductor nanomaterial (Au-ZnO and Ag-ZnO) using a new synthesis method which is green, simple and exhibiting high quantum yield and good stability nanomaterials. The first step was the synthesis of ZnO nanoparticles by a hydrothermal process in order to tune their photo-luminescence properties based on optical and structural characterization using UV-Visible spectroscopy, Differential scanning calorimetry (DSC), photoluminescence (PL) and Transmission electron microscopy (TEM). In this communication, we show results about the synthesis of ZnO nanocrystals and some ones about the hybrid nanoparticles. References [1] Jiang, R., Li, B., Fang, C., & Wang, J. (2014). Advanced Materials, 26(31), 5274-5309. [2] Wang, X., Chen, X., Thomas, A., Fu, X., & Antonietti, M. (2009). Advanced Materials, 21(16), 1609-1612. [3] Zhang, L., Wong, K. H., Chen, Z., Jimmy, C. Y., Zhao, J., Hu, C. & Wong, P. K. (2009). Applied Catalysis A: General, 363(1), 221-229. [4] Alvarez-Puebla, R., Liz-Marzan, L. M., & Garcia de Abajo, F. J. (2010). The Journal of Physical Chemistry Letters, 1(16), 2428-2434.

Resume : One of the main issues in semiconductor research is doping and crystallization. To meet the high standards of today’s microelectronic industry, especially in the context of nanostructures, more and more non-equilibrium processing technologies has been entered. This applies, above all, to thermal processing which usually has to activate dopants and anneal out defects, but has to suppress diffusion and segregation at the same time. This presentation is focused on the use of millisecond flash lamp annealing (FLA) for advanced thermal processing of group-IV materials including Si, Ge and GeSn alloys. FLA is able to exceed the solid solubility limit of dopants which is discussed for the cases of P and Sn in thin Ge films as well as for Se in Si nanowires. Moreover, the specific conditions of FLA determine whether a thin amorphous film on a crystalline substrate, e.g. an amorphous Ge layer on Ge after ion implantation, recrystallizes in a poly- or monocrystalline way. Finally, perspectives of FLA for other materials will be presented.

Resume : Si nanocrystals (Si-NCs) embedded in dielectric matrices have been extensively studied due to potential applications in novel opto- or nanoelectronic devices. To reach this goal, a deep understanding of the electrical doping of Si-NCs is, however, mandatory. Both theoretical and experimental studies have shown the possibility to dope Si-NCs with either Boron (B) or Phosphorus (P). However, the exact location of the dopants in the heavy doping regime has received only little attention up to now. In this work, we investigate heavily phosphorus doped SiO1.5 thin films prepared by evaporation under high vacuum. The films were prepared by co-evaporation of both SiO and SiO2 from e-beam guns while phosphorus was supplied by a GaP decomposition source. The structural and optical properties were studied by means of X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), Raman and Fourier transform infrared (FTIR) absorption spectroscopies. For thin films annealed at 1100°C, we provide clear experimental evidence of the formation of both SiP2 and SiP nanoparticles crystallizing in an orthorhombic structure. The overall nanoparticle size increases with the P doping from about 15 to 35 nm. STEM characterizations combined with energy dispersive X-ray spectroscopy measurements indicate that most of the nanoparticles consist of SiP2. This is consistent with Raman measurements and with density functional theory calculations of the SiP2 vibrational properties.

Resume : It has been shown that Ge nanoparticles (NPs) embedded in transparent dielectric matrix have properties different from the respective bulk semiconductor and present a great potential for application in electronic and optoelectronic devices. Due to quantum confinement properties of materials can be tuned by varying the nanoparticle size. These properties may be exploited for the fabrication of nanoscale electronic devices or advanced solar cells. Nevertheless, properties of the composite material involving NPs are not yet completely understood. In this work we explored the structural and interface characteristics of Ge NPs formed in SiC matrix. Magnetron cosputtering was used for deposition from Ge and SiC solid source, and upon suitable thermal treatment a superstructure of NPs embedded in dielectric was formed. The structural properties were explored by GISAXS/GIWAXS and Raman analysis. All techniques were used to obtain information on crystallinity, size and shape of the grown objects. Moreover, the Porod analysis of the GISAXS pattern was carried to get additional insight in the NPs / matrix interface. The results will be compared with EPR measurements. We shall explore how such layer affects PL properties of NPs.

Resume : Doping in Si nanocrystals (Si NCs) is a fundamental issue in order to develop the next generation nano-electronic and opto-electronic devices. However, achieving efficient doping in Si NCs is quite difficult since the impurities tend to be expelled from the inner sites of dots. Moreover, the introduced dopants, such as Phosphorus (P) and Boron (B) in Si NCs, exhibit the novel doping behaviors as studied previously . We have demonstrated experimentally that the phosphorus (P) dopants could incorporated into Si NCs substitutionally after passivating interface states of Si NCs in Si NCs/SiO2 multilayers. In the present work, we study the influences of P doping and P/B co-doping on the electronic and luminescence properties in Si NCs/SiO2 multilayers. It is found that the luminescence intensity around 820nm of P doped samples are enhanced by 19.4% comparing with the un-doped one which can be attributed to the P passivation effect and the nonlinear optical absorption properties of Si NC were also tuned through modifying interface states. Further, in the P/B co-doped Si NCs/SiO2 multilayers, the P doping efficiency is promoted with controlling the B co-doping level. The subband luminescence is also enhanced by co-doping. Our results suggest a new route to modulate the electronic structures and opto-electronic characteristics of Si NCs for device applications. This work is supported by NSFC (No. 11774155) and PAPD.

Resume : The common way to manipulate light consists in using classical optical elements such as lenses and mirrors. Since few years, a new way to manipulate light with two dimensional optical components, also known as optical meta-surfaces, have been exploited to control light propagation using local phase discontinuities. Owing to their reduced thicknesses and their high order of transmission in the visible, metasurface components would enable the next generation of flat optical devices. In this work, we present innovative semiconductor based metasurfaces and discuss GaN-metasurfaces manufacturing processes relevant for electronics and optoelectronics industrial applications, e.g. light-emitting diode (LED) or high-electron-mobility-transistor (HEMT).

Resume : Crystalline defects in semiconductor materials have always played an important role in the charge transport: when electrically active, they give rise to energy levels in the band gap, which serve as stepping stones for carrier recombination and generation, thus determining the lifetime. Even when they are inactive, the presence of neutral defect centers can cause scattering events, thereby affecting the carrier mobility. When entering the regime of nanodevices, the impact of defects becomes even more pronounced, as is well-known from the so-called Random Telegraph Noise (RTN) often observed in scaled MOSFETs [1]. At the same time, novel quantum effects can be amplified by the presence of defects, giving rise to potential new applications [2]. Here, the impact of single defects on the operation and the reliability of several types of devices will be discussed. Firstly, it is shown that single defect centers in Ultra-Thin Buried Oxide (UTBOX) Fully Depleted Silicon-on-Insulator (FD SOI) nMOSFETs can give rise to pronounced generation-recombination (GR) noise in the frequency domain, corresponding with RTN in the time domain [3]. It will be demonstrated that these defects play a crucial role in the retention time of single-transistor memories fabricated in UTBOX SOI [4]. Moreover, studying the characteristic frequency as a function of temperature enables to perform noise spectroscopy and assists in the identification of the deep levels, which are mainly processing induced [5]. These GR noise studies can be extended to the case of nanowire SOI FETs or to nanoscale fin-type of transistors, fabricated with so-called high-mobility channel materials (Ge, III-V) [6,7]. Similar RTN phenomena will be shown for scaled Resistive Random Access Memory (RRAM) devices based on high- dielectrics [8]. While the effects of single defects on the DC and AC transport can be experimentally assessed in a quite straightforward manner, one of the challenges is the identification of their origin. Therefore, a strategy will be discussed to tackle this challenge, which consists of a combination of spectroscopic studies on large-area devices, delivering the necessary defect parameters to implement in a Technology Computer-Aided Design (TCAD) simulation of the current-voltage characteristics of nanoscale devices [9]. [1] E. Simoen and C. Claeys, “Random Telegraph Signals in Semiconductor Devices”, Institute of Physics Publishing, Bristol, UK (2016). [2] L. Ma, W. Han, W. Hong, Q. Lyu, X. Yang and F. Yang, J. Appl. Phys. 117, 034505 (2015). [3] E. Simoen, M. Aoulaiche, S. D. dos Santos, J.A. Martino, V. Strobel, B. Cretu, J.-M. Routoure, R. Carin, A. Luque Rodríguez, J.A. Jiménez Tejada and C. Claeys, ECS J. of Solid St. Science and Technol. 2, Q205 (2013). [4] M. Aoulaiche, E. Simoen, C. Caillat, L. Witters, J. Martino, C. Claeys, P. Fazan and M, Jurczak, Solid-State Electronics 117, 123 (2016). [5] D. Boudier, B. Cretu, E. Simoen, A. Veloso, N. Collaert and A. Thean, Solid-St. Electron. 128, 109 (2017). [6] A. V. Oliveira, E. Simoen, J. Mitard, R. Langer, P. G. D. Agopian, J. A. Martino, L. Witters, A. Thean and C. Claeys, IEEE Electron Device Lett. 37, 1092 (2016). [7] L. He, E. Simoen, C. Claeys, H. Chen, D. D. Guo, L. N. Hu and Y. Qin, in the Proc. of ICNF 2017, Vilnius (Lithuania), 20-23 June 2017, IEEE Explore doi: 10.1109/ICNF.2017.7985987. [8] J. Ma, Z. Chai, W. Zhang, J. F. Zhang, Z. Ji, B. Benbakhti, B. Govoreanu, E. Simoen, L. Goux, A. Belmonte, R. Degraeve, G. Kar and M. Jurczak, submitted to IEEE Trans. Electron Devices. [9] K. Ni, G. Eneman, E. Simoen, R. Schrimpf, R. Reed, D. Fleetwood, N. Collaert and A. Thean, IEEE Trans. Electron Devices 63, 3069 (2016).

Resume : Interface dangling bonds (DBs) critically affect reliability of metal/insulator/Si devices by providing charge traps upon bias-temperature stressing. It is found, however, that adding Ge to the channel layer significantly improves the reliability and the lifetime of transistors enabling scaling to the 10 nm node and beyond. In order to get insight in the nature of this beneficial effect we analyzed DBs in Si-passivated (1- or 3-nm thick Si cap) strained-(100)Si1-xGex (x=0.25-0.55) layers at interfaces with 1.8-nm thick HfO2 dielectrics by using Electron Spin Resonance (ESR). The results suggest Si DBs (Pb0 centers) located at the interface between the Si substrate and the pseudomorphic Si1-xGex film to be the dominant defects. The density of Si DBs in the Ge containing samples is significantly lower than at the reference (100)Si/ HfO2 interface and decreases below the ESR detection limit (≈1x1011cm-2) with increasing thickness and Ge concentration in the Si1-xGex layer. However, the beneficial effect of Ge fades when the thickness of the Si cap is reduced to 1 nm or in the case of direct deposition of HfO2 on top of uncapped Si1-xGex. From these results we conclude that DBs are eliminated due to in-diffusion of Ge from the Si1-xGex channel into the Si substrate bringing the concentration of Ge to the range in which the generation of Si DBs becomes energetically unfavorable. This picture is in agreement with previous observations on condensation-grown Si1-xGex layers.

Resume : Silicon Carbide (SiC) is a wide bandgap semiconductor with superior properties, such as high dielectric strength, high thermal conductivity, high saturation velocity, and excellent physical and chemical stability. The demonstrated capability to work in harsh environment led to a rapid development of SiC based high-power electronic components and optoelectronic devices working in the ultraviolet. Nevertheless, maximum photo–responsivity in the range 240-380 nm makes SiC blind to solar radiation and does not allow an efficient exploitation of its physical properties in the solar energy conversion field. Here we demonstrate for the first time the enhancement of SiC optical absorptance obtained by femtosecond laser texturing of the surface. fs-laser pulses induce a periodic structure with a ripple period λr dependent on laser wavelength λ and material refractive index n according to λr = λ/(2n), able to drastically increase optical absorptance in the 200-2000 nm range. Moreover, we demonstrate the effectiveness of this treatment in introducing defect levels within SiC bandgap that, acting as an intermediate band, result in a significant enhancement of photo-generated current in the visible range. These outstanding results open the path for a successful exploitation of SiC for fabrication of future solar devices and for the development of efficient wide spectral range photodetectors.

Resume : We demonstrated a two-dimensional electron gas (2DEG) in a strained Ge quantum well for the first time. The Ge 2DEG was formed on a modulation-doped Ge/ Ge0.82Si0.18 heterostructure, which were epitaxially grown by reduced pressure chemical vapor deposition. Two-dimensional electrons were confined in a Ge quantum well by the Ge0.82Si0.18 energy barriers. In-situ phosphorous doping was used for the growth of the remote electron supply layer, ~ 30 nm above the QW. We fabricated the Hall-bar devices to characterize the magneto-transport properties of Ge 2DEG and Hall measurements were performed at 4 K and 0.3 K. The density and mobility of Ge 2DEG are 2×〖10〗^11 cm-2 and 1,500 cm2/Vs, respectively at 4 K. Shubnikov-de Haas oscillations with an integer quantum Hall state of υ = 1 were observed at 0.3 K. This experimental result strongly suggests the existence of 2DEG in a Ge quantum well. Along with Ge two-dimensional hole gases (2DHGs), the realization of an electron-hole bilayer system on group Ⅳ heterostructures becomes possible. Acknowledgements This work at NTU has been supported by the Ministry of Science and Technology (106-2112-M-002-009-). This work at Sandia National Laboratories has been supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, US Department of Energy (DOE). This work was performed, in part, at the Center for Integrated Nanotechnologies, a US DOE Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the US Department of Energy’s National Nuclear Security Administration under Contract No.DE-NA-0003525.

Resume : Materials consisting of silicon nanocrystals (Si-ncs) embedded in silicon dioxide (SiO2) are the subject of an intense research activity due to their numerous potential applications in the fields of optoelectronic and photonic. Moreover, the well-known and widely used process of impurity doping in such materials allows tailoring Si-based devices for a specific use. In fact, the n- or p-type dopants provide respectively electrons or holes that can significantly modify the electrical or optical properties of the materials. However, the efficiency of doped materials strongly depends on the dopant location in the host matrix. In this way, an accurate control of the dopant location is necessary in order to improve the quality of these systems. In this work, n- (P, As) and p-type (B) doping carried out by co-implantation with Si in SiO2 thin films annealed at 1100°C have been investigated using Atom Probe Tomography. In each cases, the 3D spatial distribution of Si and dopant atoms has been computed. It allowed us to study the structure of these films at the atomic scale to investigate the location of dopants and the Si clustering characteristics (size distribution, density, composition …) along the implantation profile. It has been shown that n-type dopants are efficiently introduced in Si-ncs while p-type dopant remains outside of Si-ncs. The effect of the dopant nature on the structural properties and its influence on the Si-ncs growth will be discussed.

Resume : Semiconductors having smaller and direct band gaps such as CuO, NiO etc, which show p-type conductivity and favorable conduction band alignment for hydrogen evolution from water have recently attracted attention for application as photocathode in photoelectrochemical cells. In the present study we show that sensitizing their nanostructures with low cost organic dyes, such as Mercurochrome, Eosin Y and Rhodamine-B has significant effect in enhancing their photocurrent density and hence the efficiency of hydrogen evolution reaction from water. A carrier multiplication phenomenon by dual excitation in the dye-semiconductor system has been demonstrated. The development has the potential of application not only in the field of water splitting but also in dye sensitized solar cells and other photo-redox applications.

Resume : As displays and imaging technologies become more sophisticated, development of sensors for the high-speed camera has become indispensable. Recently, image sensors for automatic operation of automobiles have become more attractive, so that not only the resolution of the sensor but also the response speed have become important. In this study, we have fabricated a vertical type photodiode using a quasi-type 2 colloidal quantum dot, which is advantageous for carrier extraction and exhibits a much faster response speed than a type 1 quantum dot. Depending on the type of ligand capping QDs, Oleic acid and MPA capped QDs showed τr = 77.6 ± 8.54 ns and τf =100 ± 14.70 ns, and τr = 28.8 ± 8.34 ns and τf = 40 ± 9.81ns, respectively. Short rise and fall times of MPA over Oleic acid capped QDs are due to short ligands in MPA than Oleic acid. A photodiode with type 2 QDs capped with MPA would be useful for the CMOS-compatible high-speed image sensors.

Resume : Sapphire is widely used as a substrate for the growth of GaN epitaxial layer (EPI), but has several drawbacks such as high cost, large lattice mismatch, non-flexibility, and so on. Here, we first employ graphene directly grown on Si or sapphire substrate as a platform for the growth and lift-off of GaN-light-emitting-diode (LED) EPI, useful for not only recycling the substrate but also transferring the GaN-LED EPI to other flexible substrates. Sequential standard processes of nucleation/recrystallization of GaN seeds and deposition of undoped (u-) GaN/AlN buffer layer were done on graphene/substrate before the growth of GaN-LED EPI, accompanied by taping and lift-off of u-GaN/AlN or GaN-LED EPI. Upconversion photoluminescence (PL) from graphene quantum dots (GQDs) excited by the second-order diffraction light of wavelength λ/2 co-existing in the red light. Real upconversion PL from GQDs is observed under excitation with a femtosecond pulsed laser, implying that coherent photons with high enough power density can be upconverted into blue light via GQDs. This approach can overcome the limitations by the catalytic growth and transfer of graphene, and make the oxygen-plasma treatment of graphene for the growth of GaN EPI unnecessary. This work was supported by a grant to the Ministry of Trade, Industry & Energy (MOTIE, Korea) under Industrial Technology Innovation Program (no.10067533), Korea Evaluation Institute of Industrial Technology, Republic of Korea.

Resume : The short-wavelength infrared (SWIR) photodetectors can be used for a variety of applications such as gas analysis, humidity monitoring, telecommunication, and spectrometry. At present, the InGaAs and extended-InGaAs photodetector is the most widely used in the SWIR band (from 0.9 to 3 µm). The cut-off wavelength (λcutoff) of InGaAs and extended InGaAs is 1.7 μm and 2.65 μm, respectively. However, in this extended InGaAs material, metamorphic growth is required to overcome lattice differences in epitaxial growth. Although many improvements related to growth have taken place, the performance at room temperature is below par and cooling is needed for higher detectivity. In the past few decades, infrared photodetectors using Sb–based structure lattice–matched on GaSb substrate have been studied and several types were developed for SWIR detection. In particular, the barrier detectors are the ability to serve as dual–band infrared detectors. It is possible to design a dual–band detector that operates independently at different spectral regions based on the bias polarity. In this study, we present the results of investigations on a dual-band detector that was fabricated using lattice–matched III–V materials, GaSb and InGaAsSb, operating in the SWIR band at room temperature. The dual-band device was grown using molecular beam epitaxy (MBE) with As2 and Sb2 cracker sources on a GaSb substrate. The active region consist of two different materials, a 2–µm–thick In0.23Ga0.77As0.22Sb0.78 and 2–µm–thick GaSb layer, which are separated by a barrier of Al0.4Ga0.6Sb ternary with thickness of 100 nm. After the epi-layer growth, the device was processed in 410×410 µm2 mesas using inductively coupled plasma etching, followed by the contact metal deposition. The devices had a circular aperture of 300 µm in each mesa. Spectral response was measured using a Fourier transform infrared (FTIR) spectrometer (Nicolet Instrument, Inc.) at room temperature with illumination from the front side of the sample. The resulting structure has detection capability in the short-wavelength infrared ranges, cut-off wavelength of 1.6 μm (SWIR1; GaSb) and 2.65 μm (SWIR2; InGaAsSb) depending on the applied bias. The dual-band photodetector was evaluated by current–voltage (I–V) characteristics, spectral response, and detectivity (D*).

Resume : A novel Silicon device composed by three integrated planar microelectrodes with the working electrode based on Nickel was developed and tested. A plastic board sealed on the top of silicon part forms electrochemical cell with a total volume of 20 µl. The sensing mechanism is based on nanosized layer of sensing active species (NiOOH) formed on top of Ni(0) working electrode by Ciclic voltammetry experiments in NaOH 0.1M. The species to detect are oxidized at electrode surface by NiOOH forming the Ni(OH)2 species, which is reconverted to NiOOH by application of an external potential (~7V) The sensing mechanism was fully characterized by analytic surface techniques such as X-ray Photoelectron Spectroscopy, Rutherford Backscattering Spectrometry and contact angle measurement. The device exhibited good response towards glucose detection on human blood and saliva samples. It is also suitable for the detection of various analytes such as, aminoacids, alchols and amines on various biological mediums such as human plasma, saliva, and urine. The experiments indicates a strong dependence of the sensitivity from the pH values, in particular the sensitivity increases with the increasing of pH value. For the detection of glucose on blood sample has been found a sensitivity at pH value 11.2 up to 40 μA/mM cm2 with a linear dynamic ranges up to 0–5 mM, while for Saliva sample a dynamic range up to 0-30mM was obtained at pH 13.0. The device shows also good performance for the detection of urinary Phenylalanine level with a good sensitivity of 0.21 μA µM-1 cm-2. The sensing tests for the detection of ethanol report a sensitivity of about 4.23 μM mg l-1 cm-2 for ethanol. A positive sensing response was also proven for the detection of molecules such as amines and diamine (useful markers for food quality), with a limit of detection of about 20 μM. References Petralia, S., Castagna, M. E., Cappello, E., Puntoriero, F., Trovato, E., Gagliano, A. and Conoci, S., Sensing and bio-sensing research 2015, 6, 90–94. S. Petralia, S. Mirabella, V. Strano e S. Conoci, Bionanoscience 7 (2017) 58-63.

Resume : SiC nanowires combine the unique properties of 1D materials with that of intrinsic SiC characteristics and offer great opportunities for UV-sensing applications. SiCNW photoelectric properties have been investigated by exposure at light sources with wavelengths of 254, 365, 532 and 633 nm. The experimental curves have been modelled to exponential rise and decay equations to determine the rise and decay time constants. CVD-grown SiCNW devices have been fabricated through dielectrophoresis onto Au electrodes with a spacing of 3µm onto SiO2/Si. The device was exposed to the 254nm UV light at 2V bias to investigate its photocurrent versus time response with irradiation lasting about 30s. The photocurrent exponentially rises to more than 80% of the saturated current within just under 2s and then reaches to steady value. The decay current took around 3s to fall down to 80% from its maximum value. Moreover, the SiCNW device did not exhibit any persistent photocurrent and showed great reversibility and recovery in photoconductance to the UV exposures. Next, the rise and decay time constants were determined to be 1.3s and 2.35s respectively, as obtained from the representative fitting curves of the photocurrent transients. A very fast photoresponse in both rise and decay processes suggests a small barrier for surface electron-hole recombination. In summary, the quick response of the SiCNW device demonstrates its potential as a photosensor for sensitive applications in photonic devices.

Resume : PIN Ge detectors have attracted a large attention due to its detection of telecom wavelength close to 1.5 micrometer. Two major concerns in this type of detector are the dark current and responsivity values. Ge has a lattice mismatch of 4% with Si, therefore a direct growth of Ge material on Si may contain high defect density which can have an impact on the detector’s performance. This article presents and compares three designs where the detectors have been processed on a virtual Ge buffer layer compared to a direct growth on Si. The Ge buffer layer has undergone a cyclic annealing to reduce the defect density in 105 cm-2. The Ge detector structure was grown selectively inside oxide openings formed on a Ge buffer layer or directly on Si substrate. The structures were either selectively grown inside oxide openings or on the entire monitor wafer followed by dry etch to form mesas. In order to remove the residual defects due to dry etch, the mesas went through an ozone treatment and the oxide was removed. The detectors had a cylindrical shape with diameter in the range of 10-100 µm. The top layer of detector was implanted by P to form the n-type layer with concentration of 1x1020 cm-3.  The contact resistance was reduced by forming of NiGe layer prior to the metallization. The metal contacts consisted of a stack of Ti/TiN/AlSi. The Ge epitaxy was carried out at 650 ºC using SiCl2H2 and GeH4 in a reduced pressure chemical vapor deposition system (RPCVD). The performance of detectors was characterized in terms of the responsivity, and dark current. The results showed a minor difference how the detectors have been grown but the contact resistance, defect density and interface quality between the grown structure and the substrate played an important role in the dark current. The dark current was increased with increasing the size of detectors. The best quality PIN structure demonstrated a dark current only a few nA which indicates state-of-art detectors.

Resume : Luminescent down-shifting (LDS) materials have optical property converting ultra-violet to visible light. We fabricated a transparent luminescent polymer-derived ceramic layer by doping LDS materials such as lanthanide complexes. Moreover, Nano-patterning of the lanthanide-doped ceramic layer enhanced the luminescence compared to reference ceramic layer. This nanostructure has low surface energy, thus enables self-cleaning of substrate. We also realized two-color emission by superimposing physically, so called a “Double imprint”. This technique offers a platform for color-tuning which can present various colors by the combination of two luminescence.

Resume : A size modified spherical cavity resonates with the incident light, leading to an increased absorption, which is called whispering gallery mode (WGM). We fabricated a photonic structure doped with spectral conversion materials (such as NaYF4: Yb, Er and quantum dot) using the Langmuir-Blodgett technique. The proposed photonic platform shows the promising result to harness the entire solar spectrum by converting both ultraviolet and near-infrared to visible light by resonant-mode coupling. The overall photoluminescence enhancements exhibit 8.5- and 12.5-fold of upconversion and downshifting luminescence, respectively

Resume : N-type semiconductor nanowires of metal-oxides are promising novel material for gas sensing applications (such as H, S, CO, O2 and others) [1,2]. The concentration of the detected gas dramatically alters electrical conductivity of the nanowire. Large surface-to-volume ratio is an advantage of the nanowires in comparison to 2D coatings. Furthermore, they can be produced on chips in large quantities to enhance the total sensitivity. We will present series of experiments on Sn and Ti thin layers. The metallic layers are grown on fused silica substrates by magnetron sputtering method. For the further experiments we use ultrathin layers with thickness ranging from 5 nm to 20 nm. The metal-oxide nanowires are formed by anodic oxidation using conductive AFM tips. We focus on finding optimal conditions for the preparation of nanowires by varying AFM parameters (applied force, anodic oxidation velocity and applied voltage), initial layer properties thickness and the length of the nanowires. The nanowires are produced in a gap between two platinum electrodes. The electric properties of the nanowires are tested in dependence on their length and gas concentration. Moreover, the nanowires are characterized by SEM-EDS (elemental mapping) to gain their homogeneity and TEM to clarify their nanostructure. [1] Kolmakov A. et al, Adv. Mater. 2003, 15, No.12, 997-1000 [2] Dai Z. R et al, J. Phys. Chem. B 2002, 106, 1274-1279

Resume : The nanopowders (NPs) (ZnO, TiO2) were obtained using the pulsed laser ablation of metallic target (Zn, Ti) in a mixture of reactive (O2) and inert (Ar) gases. The structural and optical properties of the NPs were investigated by X-ray diffractometry, electron microscopy, photoluminescent (PL) and Raman spectroscopy. Studies of the dependence of the intensity of PL of ZnO and TiO2 NPs on the wavelength of excitation including in gases has been carried out and the optimal wavelengths to excitation the visible luminescence are established. On the PL spectra of ZnO NPs, the peak centered at 387 nm with increase in the excitation wavelength from 220 nm to 350 nm, there is a smooth growth of the intensity of the luminescence followed by a sharp increase in its approach to exciton excitation. For other PL band centered at 525 nm when the excitation energy (225<λ<265 (nm)) is much larger than the bandgap there is a smooth increase in the emission intensity. With increasing of the excitation wavelength up to 375 nm, there is a slight decrease in emission and the reveal of sharp peak at 380 nm, which corresponds, apparently, to exciton excitation energies. The next increasing of the excitation wavelength characterized by a sharp decline in PL intensity until its complete quenching at 400 nm. For TiO2 NPs the PL spectra are characterized by an increase in the visible emissions intensity with the excitation wavelength increases from 265 to 405 nm without a noticeable change in the character of the spectrum itself. Based on the phonon bands (mode) analysis in the Raman spectrum of ZnO and TiO2 NPs the character of the quality of the crystal structure are determined and their evolution in the process of laser annealing. The obtained research results were effectively used to increase the selectivity of the gas sensor system by changing the UV excitation wavelength.

Resume : Abstract: ZnO nanoparticles were synthesized using sol-gel method. The influence of the annealing temperature on the structural, morphological and optical properties of ZnO nanoparticles is studied. The properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), Uv-Vis spectroscopy and EDS. XRD analysis demonstrates that the crystallinity of ZnO is improved with annealing for all growth temperatures selected (45, 55 and 65 °C) as indicated by narrower and more intensified diffraction intensities of the annealed ZnO compared to that of the as prepared particles. The average crystallite sizes of the ZnO particles increased from 29.9 nm to 33.3 nm with annealing indicating the tendency of large grain growth in the nanoparticles due to annealing. SEM micrographs showed that annealed ZnO nanoparticles aggregated and became larger in diameter compared to its as prepared counterparts. The EDS analyses, for as prepared and annealed samples indicate the purity of all the synthesized samples with no peaks other than Zn and O. The photoluminescence peak intensity ratios of ultraviolet to that of visible emission (UVPL/ VisPL) are found to increase on annealing. The UVPL/ VisPL intensities ratio range between 0.9-2.4 for the as prepared samples and 5.0-7.1 for annealed samples. Quenching of visible emission on annealing is known to be responsible for this. The red shift in both the visible and UV emission with increasing particle size due to annealing closely follows the red shift in the band edge emission, indicating that the two complement each other. The average band gap is observed to decrease from 3.25 eV to 3.22 eV with the increase in crystallite sizes occasioned by annealing. Keywords: ZnO; Nanoparticles; Sol-gel; Growth temperature, Structure, Luminescence

Resume : Here we propose an innovative mechanism to detect physiological signals (specifically the PhotoPlethysmoGraphy(PPG) signals) of the driver by means of specific silicon detectors placed on the car steering, composed by a silicon photomultipliers SiPMs having a total area of 4.0x4.5 mm2 and 4871 square microcells with 60 μm pitch coupled in transmission with two OSRAM LT M673 LEDs in SMD package as optical light source. The PPG signal of the driver is reconstructed each time hands are placed on the car steering through the changes on the oxygenated/de-oxygenated hemoglobin captured by the SiPM based sensor. By means of ad-hoc innovative mathematical pipeline based on that nonlinear model, we are able to identify compliant and robust PPG waveforms on the driver PPG signal[1,3]. The described post-processing PPG signal will be performed in a near real-time range compatible with automotive system constraints. Ad-hoc innovative analysis of the post-processed PPG driver signal will be performed in order to establish the driver drowsiness level and, consequently, perform the proper action in order to keep car and driver safety. References [1] F. Rundo, S. Conoci, et al, “PROCESSING OF ELECTROPHYSIOLOGICAL SIGNALS”, IT Patent Nr. 102017000081018, 18 July, 2017; [2] F. Rundo, S. Conoci, et al, “A METHOD OF PROCESSING ELECTROPHYSIOLOGICAL SIGNALS, CORRESPONDING SYSTEM, VEHICLE AND COMPUTER PROGRAM PRODUCT”, IT Patent Nr. 102017000120714, 24 October, 2017; [3] F. Rundo et al “Progresses towards a Processing Pipeline in Photoplethysmogram (PPG) based on SiPMs“, IEEE Proceedings of 23 European Conference on Circuit Theory and Design, Catania(Italy) 4-6 September 2017;

Resume : Since the invention of the first Lab-on-Chip system in the 1979, the miniaturization, the ability to move small volume sample into microstructures and to perform biological reaction have become indispensable for molecular diagnostics and sensing applications. Here is described a miniaturized system composed by a silicon microchip able to electrically deliver a sample volume of 20µl of liquid into miniaturized 96 silicon microchambers 200nl each in volume. The device contains also integrated temperature sensors and heaters for thermal driving. The silicon microchambers are chemically treated by a specific surface chemistry to permit the liquid movement. The coating was properly engineered to permit the switching from hydrophobic surface with a static contact angle value of about 110°, to hydrophilic surface with a static contact angle value less than 5°, by an external electrical filed application. An electrical conductive polycarbonate structure was properly engineered to permit the external electric field application. The entire hybrid structure (polycarbonate and silicon chip) is connected to a circuit board that drives the chip through a specific software that is also able to analysed the collected data. A CCD camera is also embedded to monitor the liquid movement. Thanks to the integrated silicon temperature sensor and heaters, the chip allows a temperature control accuracy of ± 0.2 °C, heating rate of 15 °C/s and cooling rate of 8 °C/s. This system very appealing for gene expression applications in miniaturized PCR lab-on-a-chip, where both very small volume (about 20uL) and high number of chambers (>100) are required.

Resume : The miniaturization of device able to perform nucleic acid detection by Real time PCR method is a key point to develop the“genetic point-of-care” system for sample-in-answer-out analysis. In this scenario an innovative Lab-on-Disk system was developed for the detection of pathogen nucleic acids (DNA). The miniaturized system is composed by a hybrid silicon-polycarbonate chip with six OR 12 microchambers, embedded on a polycarbonate holder with four chip position and a reader for the real time PCR thermocycling experiments. The hybrid silicon-polycarbonate device manufactured by standard semiconductor technology integrates in the silicon part the heaters and temperature control sensors to perform thermal cycles with an accuracy of 0.1 °C, the polycarbonate part is glued with silicon part to form the microchambers. A customized and easy-to-use reader integrates an electronic board to driven the silicon device and the optical module for RT-PCR fluorescence images acquisition. Two different wavelength (FAM and VIC) are available. This work reports the experimental results for the detection of Hepatitis Viruses B (HBV) genome. The results indicate an good improvement of sensitivity ( about 1 cycle threshold) respect to the commercial RT-PCR platforms. This improvement is an important features for application on infectious disease where the amount of pathogen genome is very low. This straightforward improvement on sensitivity is mainly due to the particular microchambers shape and reader performance. References S. Petralia, and Sabrina Conoci. ACS Sensors. 2017, 2, 876. S. Petralia, M. E. Castagna, M. O Spata, M. G. Amore and S. Conoci Biosens J, 2016, 5:1 S. Petralia, E. L. Sciuto, M. L. Di Pietro, M. Zimbone, M. G. Grimaldi and S. Conoci. Analyst, 2017, 42, 2090.

Resume : We have theoretically investigated the 1.55 µm p-i-n GaNAsBi-based multiple quantum wells (MQWs) using a self-consistent calculation combined with 16x16 BAC model. Their performances are evaluated in terms of optical gain and radiative current density J_rad. We have found that J_rad reduces by increasing the well thickness〖 L〗_ω. The quantum confined Stark effect as well as the doping effect on spontaneous emission and radiative current density in ideal lasers are also discussed. The optical properties of the heterostructure are improved when the MQWs are doped. The optimization of well parameters can be used as a basis for GaNAsBi-based lasers intended for optical fiber telecommunication wavelength.

Resume : Silicon physical properties, easy manufacturing and cheapness promoted its industrial employment as a leading material for different applications. Si indirect bandgap is a great limit for photonics and the scientific community has devoted efforts on the realization of a new class of efficient light emitters based on Si platforms. By a low cost and industrially compatible method, we realized ultrathin and dense vertical array of Si nanowires (NW) that efficiently emit light in the visible at RT due to quantum confinement. Fractal arrays of Si NWs exhibiting a strong light trapping from visible to near-IR were synthesized without any lithography or mask. We engineered the realization of multi-wavelength light sources operating at RT by decorating fractal Si NW with Er doped yttrium oxide deposited by sputtering in oblique angle deposition configuration by placing the substrate at different angles with respect to the normal direction to the target. Er in yttrium oxide is characterized by intense IR emission strategic for telecom applications. The structural properties and fractal parameters were characterized as a function of deposition settings and correlated to the optical properties. By using different excitation wavelengths, we demonstrate the Er emission is enhanced by scattering effect driven by the fractal morphology of the NW array. This material opens new perspectives for Si platform as active medium in light sources for Si photonics and telecommunication applications.

Resume : Photopletysmography (PPG) is a very common optical approach to measure blood oxygen levels for patient monitoring as well as heart rate in fitness tracking devices. In the transmission mode the use of amorphous silicon photodiodes falls short of other solutions because the light sources are selected in the red and near infrared region of the spectrum, where the sensitivity of photodiodes is limited, to obtain better transmission through human tissue. Nevertheless, a number of studies have shown that reflection mode PPG using visible light is also an interesting option due to the reduction of motion artifacts, which can be critical in sports applications and portable medical devices. In this region of the spectrum an amorphous silicon photodiode provides an interesting solution due to its sensitivity and low fabrication cost using Plasma Enhanced Chemical Vapor Deposition (PECVD) In this study we use a double junction amorphous silicon photodiode for PPG in the reflection mode. The active device is a double photodetector produced by PECVD. It consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure with high resistivity doped layers packed between two transparent oxide layers (TCO) made of ITO. The energy gap and semiconductor properties of each junction have been selected to provide sensitivity across the visible range. The photodiode can be electrically biased to tune for different wavelengths. This can be of particular interest for PPG where there is a trend towards increasing the number of wavelengths using multiple LEDs not only to improve the accuracy of SpO2 measurements, but also to provide real-time measurements of other substances in blood. We describe the physical and optical characteristics of the photodiode that make it useful for this application and have developed a test prototype to assess it, which includes the LED control system and the signal conditioning circuit for acquisition of the PPG signals. The results allows to define wavelengths of interest taking in consideration the sensitivity of the photodiode and regions of operation in terms of switching frequency of the LEDs.

Resume : In this paper we present an improved architecture for silicon plasmonic hot electron detector with high responsivity in the SWIR range. Hot electron devices consist typically of a metal surface in contact with a semiconductor forming a Schottky barrier. Hot electrons generated in the metal layer from the nonradiative decay of surface plasmons (SPs) can be emitted (internal photoemission process- IPE) over the barrier into the semiconductor if their energy is higher than the Schottky barrier. IPE enables sub-bandgap photodetection making thus silicon devices suitable for operation in the NIR-SWIR ranges. However the efficiency of IPE process is low due to the momentum mismatch between the bound surface plasmon and the free propagating incoming photons. To allows incident light to be momentum matched and efficiently coupled to SPs we used corrugated electrodes. We developed a simple process for the fabrication of plasmonic corrugated structures without using costly and time-consuming nano-lithographic processes. The process is based on vacuum deposition of very thin Ag layer followed by thermal annealing. A periodic structure composed of flattened nano-hemispheres is obtained. The diameter and the high of the nanostructures depend on the initial thickness of the Ag layer and on the annealing process parameters. The corrugated Ag layer acts as metamaterial absorber that improves the efficiency of hot electrons generations. The devices show very high resposivities, up to 12 mA/W at 1550 nm, among the highest reported. The device bandwidth can be tuned by modifying the geometry of the metamaterial. Acknowledgments: The work was supported by a grant of the Romanian Ministry of Research and Innovation, project PN-III-P2-2.1-PED-2016-0307.

Resume : The optical properties of InAs quantum dots with two different strain-reducing layers (SRLs) were characterized using photoluminescence (PL). The used SRLs are GaAs1−xSbx(x=6%) and InyGa1−yAs1−xSbx (x=1.2%, y=14%). A longer emission wavelength with InAs/InGaAsSb QDs has been identified. It reaches 1406 nm and 1340 nm for ground and first excited state at room temperature, favoring the application of the ES quantum dot laser in optical-fiber communications. Variation of PL peak energies and full width at half maximum of the QDs ground state transition as a function of excitation density were studied. Dependence of the integrated PL intensity as a function of the excitation density at different temperatures was also studied. For low temperature and low excitation density, the integrated PL intensity increases nearly linearly with excitation (slope is slightly lower than unity) in all samples. This linear dependence is typical for localized excitons. Further, the increase of the excitation power density results in a superlinear dependence (slope is between 1 and 2). Indeed, the increase of the excitation power at low temperature favors the filling of the localized states and allows the excitons to recombine non-radiatively. With increasing temperature, superlinear dependence is conserved and even increased slightly. This behavior is explained by the thermal energy which becomes comparable to the binding energy of excitons that can be dissociated and recombine as free carriers.

Resume : Semiconductor NWs have been proven to be useful as basic building blocks for photonic components, including lasers, detectors, modulators and solar cells. Silicon is the most important semiconductor and the possibility to obtain an efficient room temperature light emission from Si NWs would represent an important advancement in photonics. In spite of this great potential interest, light emission from Si NWs is still a scarcely reported and unexplained phenomenon. We will present a new approach for Si NWs synthesis, based on a metal-assisted wet etching process. The process is simple, cheap, fast, compatible with Si technology and, above all, able to synthesize Si NWs exhibiting a strong room temperature photoluminescence (PL). We will present a detailed analysis of the steady-state and time-resolved PL properties of the system as a function of aging, temperature and pump power to demonstrate that the emission is due to the occurrence of quantum confinement effects. Moreover, we will present a prototype device based on Si NWs exhibiting a strong and stable room temperature electroluminescence at operating voltages as low as 2 V. These results open the route towards novel photonic applications of silicon NWs as efficient light sources.

Resume : Nowadays, nanomaterials are widely employed as substrates in laser desorption/ionization mass spectrometry (LDI-MS) analysis of small molecules [1]. Among different materials, silicon nanowires (SiNWs) are recognized as efficient substrates thanks to the reduction of background interference below 1000 m/z, at low laser fluence [2]. Here, we report on the successful LDI-MS application of SiNWs prepared by a mask-less wet-etching protocol at room temperature followed by their decoration with silver nanoparticles (AgNPs), produced by pulsed laser deposition. Such hybrid systems (AgNPs@SiNWs) are extremely active substrates, especially towards analytes bearing unsaturated bonds. Free fatty acids in vegetable oils can be investigated through this approach without severe sample pretreatment [3]. Moreover, surface chemical characterization confirmed that nanostructured Ag(0) was present on the surface. [1] R.A. Picca et al., Nanomaterials 7 (2017) 75, doi:10.3390/nano7040075. [2] M. Dupré et al., Analytical Chemistry 84 (2012) 10637. [3] R.A. Picca et al., Journal of Mass Spectrometry 51 (2016) 849.

Resume : The high aspect ratio of Si nanowire (NW) arrays has a great potential for many applications and in particular for Si-based sensors. For this purpose, we coupled the huge surface-to-volume ratio of Si NW to plasmonic effects decorating the NW array with metal nanoparticles (NPs). Si NWs were synthesized by metal-assisted chemical etching and then decorated with silver nanoparticles (NPs) produced by pulsed laser deposition (PLD). Both NW synthesis and decoration techniques are performed at room temperature with a low-cost and Si implementable technology. The obtained Ag NP decorated Si NWs are free from chemicals contamination and there is no need of post deposition high temperature processes. The results show that this approach allows the full coverage of the Si NW walls with a strong control on the Ag NP size and distribution. The optical properties of Si NW arrays were investigated by reflectance spectroscopy showing the presence of a plasmon absorption peak dependent on the Ag NP morphology. The great potentialities of PLD metal decoration of Si NWs for surface enhanced Raman spectroscopy (SERS) applications are reported as a function of rhodamine 6G (R6G) concentration in aqueous solution. A very low limit of detection of 10−8 M was demonstrated and a SERS enhancement factor of 108 of about one order of magnitude higher with respect to a similarly decorated Si flat surface was estimated.

Resume : Si-based multiwavelength light sources are of great interest for applications in photonics and multiplexed signal communication. The realization of an innovative hybrid light source operating at room temperature, obtained by embedding a carbon nanotube (CNT) dispersion inside a Si nanowire (NW) array is reported. Ultrathin Si nanowires (NWs) synthesized by metal assisted chemical wet etching using a very thin discontinuous Au layer as precursor were used as platform and coated with debundled single walled carbon nanotube (CNT) dispersions. A bright room temperature emission in the visible range due to electron–hole recombination in quantum confined Si NWs is reported. The hybrid Si NW/CNT system exhibits a room temperature simultaneous emission both in the visible (due to Si NWs) and the IR (due to CNTs) ranges, thus demonstrating the realization of a low-cost material with promising perspectives for applications in Si-based photonics. The detailed study of the optical properties of the hybrid system evidences that the ratio between the intensity of the visible and the IR emissions can be varied within a wide range by changing the excitation wavelength or the CNT concentration and the conditions leading to the prevalence of one signal with respect to the other were investigated. The multiplicity of emission spectra obtainable from this composite material opens new perspectives for Si nanostructures as active medium in light sources for Si photonics applications.

Resume : Two-dimensional (2D) materials, layered crystals with strong intra-layer covalent bonds and weak inter-layer van der Waals coupling, have been of great interest recently within the scientific community. While 2D materials possess many unique properties, it remains an open question for which applications these materials can truly provide a benefit compared to conventional solutions. Here, I describe our work on 2D materials, and discuss potential applications in electronics, sensing and spintronics where these materials have the potential to provide improved and/or novel functionality compared to the state of the art. Graphene, a single sheet of sp2-bonded carbon has extremely high mobility, but its zero-gap band structure makes it poorly suited for conventional field-effect transistors. Instead we have shown that numerous other properties of graphene can be utilized to create new types of devices. For instance, we have shown that the quantum capacitance in graphene can be utilized to realize variable capacitor (varactor) sensors [1,2]. These sensors have the potential for small size, multiplexed sensing capability, and most importantly, wireless readout capability [3]. More recently, we have shown that graphene edges can form atomically sharp “tweezers” for trapping biomolecules such as DNA [4]. Due to the atomic-scale sharpness of graphene, this trapping can occur at extremely low voltages (as low as 700 mV), making them suitable for integration with on-chip electronic reado

Resume : Among many innovative approaches proposed to increase the silicon Solar Cell (Si-SC) efficiency, the frequency conversion layer which spectrally redistributes the irradiance from either direct sun light in case of Down Conversion (DC) or Down Shifting (DS) layers or from transmitted and back reflected light in case of Up-Conversion (UC) layer is promising. Thus, frequency conversions may increase SC efficiency at the expense of the thermalization of generated carriers due to the improved spectral overlapping between the irradiance and the Si-SC absorptivity. Those mechanisms are often based on absorption and emission of trivalent Rare Earth (RE) ions. Thus for DC process couples of ions such as Tb3 (Pr3 )-Yb3 are used while for the DS one, ion such as Pr3 or Tb3 has been tested. Unfortunately, RE ions major drawbacks are their low excitability by solar irradiance and chemical incompatibility of usual host matrix with Si-SC process. The purpose of this paper is to present the fabrication and study of DC (DS) homogenous and superlattice layers which consist in a Si-based matrix doped with Tb3 (Pr3 )-Yb3 ions fabricated by a co-sputtering approach. High conversion efficiency DC (DS) layers were structurally and optically characterized. Modelling by means of Monte Carlo approach and by rate equations model allowed us to better understand the role of RE ions interdistances on the energy transfer mechanism and consequently on the efficiency of the frequency conversion.

Resume : Time-resolved photoluminescence spectroscopy is a powerful tool for examining the dynamics of optically active materials. At the standard fiber communication wavelengths of 1.5 microns such experiments can be carried out using commercial InP/InGaAs photomultiplier tubes. However, at longer wavelengths, relevant for e.g. the recent developments within GeSn laser materials, other techniques must be employed. Here we report on our work using non-linear optics for upconverting long-wavelength photoluminescence into short-wavelength light detectable by standard silicon-based detectors with nanosecond time resolution.

Resume : The outstanding excitonic properties, including photoluminescence quantum yield (PLQY), of individual, quantum-confined semiconductor nanoparticles are often significantly quenched upon aggregation, representing the main obstacle towards scalable photonic devices. Here we report aggregation-induced emission (AIE) phenomena in the lamellar solids containing layer-controlled colloidal quantum wells (CQWs) of hybrid organic-inorganic lead bromide perovskites, resulting in anomalously high solid-state PLQY of up to 94%. Upon forming the QW solids, we observe an inverse correlation between exciton lifetime and , clearly distinct from that in typical quantum dot solid systems. Our multiscale theoretical analysis reveals that in a lamellar solid, the collective motion of the surface organic cations are more restricted to orient along the [100] direction, thereby inducing a more direct bandgap that facilitates radiative recombination. Using the QW solids, we demonstrate ultra-pure green emission by completely downconverting a blue GaN light emitting diode (LED) at room temperature, with a luminous efficacy higher than 90 lm/W at 5,000 cd/m2, which has never been reached in any nanomaterial assemblies by far.

Resume : Mono-crystalline diamond needles are quite attractive samples for field emission applications, mainly used as point electron source. The performances of these electrons sources change from one needle to another. These changes could be related to a variation in the electrical conduction therefore we used a new experimental setup to study the conduction properties of diamond nano-needles in a large range of emission currents and under femtosecond laser illumination. The experimental setup is a field ion microscopy (FIM), equipped with an energy analyzer and a amperemeter, used to measure the emitted ion current at the needle apex and the energy of these emitted ions. Changing the voltage applied to the nanoneedle, we exhibited two different conduction behaviors: a first regime, at low emission current, which corresponds to the ohmic conduction and a second regime, at high emission current, which corresponds to a Poole-Frenkel (PF) conduction mechanism. We discuss the transition between these two conduction mechanisms and its dependence as a function of the emitted current and the needle geometry. Under femtosecond laser illumination, the resistivity changes and the transition from the ohmic conduction regime to the PF regime is observed at higher emission currents. The study of the changes of the conduction parameters under illuminations allows us to draw conclusion on the optical absorption process of these nanoneedles and on their heating induced by laser illumination.

Resume : Introduced by Allen et al., it has been realized that light can carry orbital angular momentum (OAM) in addition to the spin angular momentum (SAM). Independent of the polarization state, light with an azimuthal phase dependence of exp(ilφ) has OAM lћ per photon. The value of l (the topological charge), as a new dimensionality, can be valued with any integer. Having l spiral phase fronts and a transverse component of the Poynting vector perpendicular to the propagating direction, such kind of light is also known as optical vortex. Aim to explore the benefit introduced by optical vortex, we have proposed and demonstrated several photonic integrated devices. In this article, some representative devices of our recent work would be briefly introduced. They are the integrated “Cobweb” emitter with a wide switching range of OAM modes, integrated “Cogwheel” emitter to generate optical superimposed vortex beam and plasmonic vortex devices. (1) Integrated “Cobweb” emitter with a wide switching range of OAM modes. The independence of the micro-ring cavity and the gratings unit provides the flexibility to design the device and optimize the performance. Specifically, the dynamic switching of 9 OAM modes (l = –4~4) with azimuthal polarization has been demonstrated with electrically controlled thermo-optical effect (Scientific Reports 6: 22512, (2016)). (2) Integrated “Cogwheel” emitter to generate optical superimposed vortex beam with tunable OAM. With fixed wavelength and power of incident beam, the OAM of the radiated optical superimposed vortex beam can be dynamically tuned. The experimental results confirm the tunability of superimposed vortex beams with topological charge of l=-5~5. (3) Plasmonic vortex devices: As a fundamental tool for light-matter interactions, plasmonic vortex (PV) is extremely attractive due to its unique near field properties. However, it is hard to dynamically and continuously tune the OAM carried by PVs and the properties of fractional PVs are still not well investigated. We have proposed a novel method of utilizing the propagation induced radial phase gradient of incident Laguerre-Gaussian (LG) beam to sculpture PVs from integer to fractional OAM dynamically. Furthermore, a series of plasmonic devices are proposed to generate multi-patterned and two-dimensional optical lattice with helicity or not. Due to spin-orbit coupling, both the spin and orbital angular momentum of incident beam as well as the excited polygonal plasmonic mode contribute to the formation of optical lattice. With the compactness and flexible tunability, we believe that this work would facilitate the utilization of optical lattice in various on-chip applications.

Resume : Performances of silicon integrated circuits (ICs) are limited by wire delay and power consumption, but might be improved by the introduction of optical techniques. Combining plasmonic circuits with silicon ICs is one solution; however, surface plasmon signals suffer from larger transmission losses than electrical and optical signals. Here, we discuss the applicability of plasmonic ICs to silicon substrates in terms of energy loss and transmission speed. The signal transmission speed in plasmonic ICs, which is determined by the circuit dispersion, was about two-orders of magnitude higher than that of electrical ones determined by circuit capacitance and resistance. We compared the transmission energy losses in plasmonic waveguides and electric wirings and clarified that plasmon signals are superior to electric signals if suitable waveguide structures are selected and the area of the circuit is within a few hundreds of micrometers. We developed various plasmonic components, based on CMOS-compatible processes, for merging with silicon ICs. These components consist only of materials used in silicon ICs. Plasmonic signals were transmitted, modulated, used for logic operation, and detected in the circuits without any additional components. The scales of each component were of less than a few tens of micrometers, and these results suggest promise for the integration of plasmonic components into silicon ICs.

Resume : Light management and surface passivation has become an important aspect to improve the performance of solar cells, particularly based on thinner wafers and foils. Hence, we develop unique three-dimensional (3-D) dielectric photonic (nanocones and gratings) structures (PS) in SiO2 layers that efficiently trap light in silicon cells. The PS were designed using simulations. The PS of SiO2 were developed using nanoimprint lithography based on commercial silica gel layer. The nanostructures showed a high optical transmittance of > 95 %. The aspect ratio of PS varied with the processing conditions and grating showed a height profile of 450 nm while it is ~200 nm for cones. The PS showed a minimum reflectance of 15 % in the visible wavelength range. The as-deposited dielectric PS on n-type silicon showed considerable passivation and its quality improved to a minority carrier lifetime of 287 s at an injection level, 10E15 cm-3 after a short annealing in forming gas. The study demonstrates a promising approach for designing a variety of photovoltaic devices, particularly flexible crystalline silicon solar cells.

Resume : A VLC indoor positioning system that uses white RGB-LEDs for both illuminations proposes and as data transmitters is presented. The receiver is implemented using a double p-i-n/pin SiC photodetector with light filtering properties. An OOK modulation scheme is used to modulate the light. Optoelectronic characterization of the transmitter and receiver are performed. A detailed analysis of the component’s characteristics within the VLC system, such as multiplexing techniques, visible light sensing, indoor localization and navigation recognition were discussed. LED bulbs work as transmitters, sending information together with different identifiers, IDs, related to their physical locations. Square and hexagonal topologies for the unit cell are tested, and a 2D network localization design, demonstrated by a prototype implementation, is presented. The key differences between both topologies are discussed. Fine-grained indoor localization is tested. The received signal is used in coded multiplexing techniques for supporting communications and navigation concomitantly on the same channel. The position of the device is estimated by measuring the strength of the MUX signal from several transmitters. The location and motion information is calculated by position mapping and estimating the location areas. For both topologies, the transmitted data information, indoor position and motion direction of the mobile device are determined.

Resume : White LEDS revolutionized the field of illumination technology mainly due to the energy saving effects. Besides lighting purposes LEDs can also be used in wireless communication when integrated in Visible Light Communication (VLC) systems. Indoor positioning for navigation in large buildings is currently under research to overcome the difficulties associated with the use of GPS in such environments. In this work it is proposed an indoor navigation system based on the use of VLC technology. The proposed system includes tri-chromatic white LEDs with the red and blue chips modulated at different frequencies and a pinpin photodetector with selective spectral sensitivity. Optoelectronic features of both optical sources and photodetector device are analyzed. The photodetector device consists two pin structures based on a-SiC:H and a-Si:H with geometrical configuration optimized for the detection of short and large wavelengths in the visible range. Its sensitivity is externally tuned by steady state optical bias. The localization algorithm makes use of the Fourier transform to identify the frequencies present in the photocurrent signal and the wavelength filtering properties of the sensor under front and back optical bias to detect the existing red and blue signals. The viability of the system was demonstrated through the implementation of an automatic algorithm to infer the photodetector cardinal direction.

Resume : In this work, the impact of different Ge PAI on the formation of ultrathin TiSix films as well as on the specific contact resistivity in TiSix/n-Si contacts were investigated systematically. Extensive material characterizations such as cross-sectional transmission electron microscopy (XTEM), X-ray diffraction (XRD) and angle-resolved X-ray photoelectron spectroscopy (ARXPS), as well as electrical characterizations such contact resistivity values, Schottky barrier height (SBH) and leakage current of p-n junctions, were performed. It is found that Ge PAI indeed promotes the Ti silicidation at 550 oC and the resultant tTiSix values are strongly dependent on the thickness of amorphous Si (t-Si) created by Ge PAI. The stoichiometry of TiSix films is rather graded than constant from the TiN/Ti side to Si side. Proper Ge PAI is beneficial in reducing the c values in TiSix/n-Si contacts and this reduction in c cannot attributed to the reduction of SBH. Though proper Ge PAI leads to reduced c values, the leakage current of p-n diodes is increased as a penalty which needs to be compromised in practical applications.

Resume : The modern electronics have been built upon the solid basis of bulk crystalline silicon (c-Si), which is, however, a brittle semicondutor that has little stretchability. So far, most of the stretchable electronics have been prototyped and fabricated with polymer and organic semiconductors, which usually offers poorer electronic characteristics compared to those of c-Si based devices, particularly in terms of carrier mobility, passivation and stability in air/humidity exposure. In order to extend the legend of c-Si into the emerging application of soft electronics or bio-sensors applications, line-shape engineering has been a key strategy to endow extra flexibility and stretchability to quasi-1D silicon nanowires (SiNWs) channels. We here explore a self-assembly in-plane solid-liquid-solid (IPSLS) growth of SiNWs,[1-4] where a thin film of amorphous Si (a-Si) is fed as precursor layer to drive the indium (In) or tin (Sn) nano-droplets to move and produce well-defined crystalline SiNWs behind. The line-shape of the in-plane SiNWs can be engineered either via a self-automated zigzag growth, stimulated by a strong interface squeezing interaction during the in-plane growth,[5] or via a deterministic line-shape programming of in-plane SiNWs into extremely stretchable springs or arbitrary 2D patterns, with the aid of a precise guided growth along programmed step edges.[6] A reliable and faithful single run growth of c-SiNWs over turning tracks with different local curvatures has been well established, while high resolution transmission electron microscopy analysis reveals a high quality mono-like crystallinity in the line-shaped engineered SiNW springs. Excitingly, in situ scanning electron microscopy stretching and current-voltage characterizations also demonstrate a super-elastic and robust electric transport carried by the SiNW springs even under large stretching of more than 200%. This highly reliable line-shape programming approach holds a strong promise to employ the mature c-Si technology for the development of a new generation of high performance bio-friendly and stretchable electronics. As an example, we will also demonstrate a highly stretchable networks of continuous c-Si springs and explore their applications for bio-sensing on curvilinear human skin or tissue surface. References [1] L. Yu, P.-J. Alet, G. Picardi, P. Roca i Cabarrocas, Phys. Rev. Lett. 2009, 102, 125501. [2] L. Yu, P. Roca i Cabarrocas, Phys. Rev. B 2010, 81, 085323. [3] M. Xu, Z. Xue, J. Wang, Y. Zhao, Y. Duan, G. Zhu, L. Yu, J. Xu, J. Wang, Y. Shi, C. Kunji, P. Roca i Cabarrocas, Nano Lett. 2016, 16, 7317. [4] Z. Xue, M. Xu, Y. Zhao, J. Wang, X. Jiang, L. Yu, J. Wang, J. Xu, Y. Shi, K. Chen, P. Roca i Cabarrocas, Nature communications 2016, 7, 12836. [5] Z. Xue, M. Xu, X. Li, J. Wang, X. Jiang, X. Wei, L. Yu, Q. Chen, J. Wang, J. Xu, K. Chen, P. Roca i Cabarrocas, Adv. Func. Mater. 2016, 26, 5352. [6] Z. Xue, M. Sun, Y. Zhao, Z. Tang, T. Dong, J. Wang, X. Wei, L. Yu, Q. Chen, J. Xu, Y. Shi, K. Chen, P. R. i. Cabarrocas, Nano Lett. 2017, 17, 7638.

Resume : Group IV nanostructures, particularly of Ge nanocrystals (NCs) embedded in oxides are promising candidates for photo-effect applications such as photosensing, photovoltaics, light emission and photocatalysis. This is mainly due to the advantage of controlling spectral sensitivity limit by changing the NC size. In this work, we investigate the optical, electrical and photoconductive properties in correlation with the structure properties and morphology of Ge NCs embedded in TiO2 films prepared by magnetron sputtering deposition and subsequent nanostructuring by rapid thermal annealing. For this we use different characterization methods of high resolution transmission electron microscopy, X-ray diffraction, optical transmission and reflectance as well as dark and photocurrent measurements. We evidence different phenomena related to Ge NCs: i) the refractive index shows a deep minimum related to NCs formation; ii) the optical bandgap of Ge NCs is correlated with their size proving the blue-shift due to quantum confinement; iii) Efros-Shklovskii Coulomb-gap variable range hopping is found to be responsible for the temperature dependence of the dark current; iv) the photoconduction is enhanced by the formation of Ge NCs in comparison to the one of as-deposited amorphous films. More than that, we demonstrate the enhancement of photocurrent by field effect that controls the Fermi level at the film-substrate interface.

Resume : The paper proposes the use of Visible Light Communication (VLC) in Vehicular Communication Systems for vehicle safety applications. A smart vehicle lighting system that combines the functions of illumination, signaling, communications, and positioning is presented. The system aims to ensure the communication between a LED based VLC emitter and an on-vehicle VLC receiver. A traffic scenario is stablished. Vehicle-to-vehicle (V2V) and Infrastructure-to-Vehicle (I2V) communications are analyzed. For the V2V communication study, the emitter was developed based on the vehicle head lights, whereas for the study of I2V communication system, the emitter was built based on streetlights. The VLC receiver is used to extract the data from the modulated light beam coming from the white RGB-LEDs emitters. The VLC receiver is based on amorphous SiC technology and enhances the conditioning of the signal enabling to decode the transmitted information. The [p(SiC:H)/i(SiC:H)/n(SiC:H)/p(SiC:H)/i(Si:H)/n(Si:H)] tandem photodetectors are located at the roof-top of the vehicle, for I2V communications, and at the tails for V2V reception. Clusters of emitters, in a square topology, are used in the I2V transmission. The information and the ID code of each emitter in the network are sent, simultaneously, by modulating the individual chips of the trichromatic white LED. Free space is the transmission medium. An on-off code is used to transmit data. An algorithm to decode the information at the receivers is set. The proposed system was tested. The experimental results, confirmed that the proposed cooperative VLC architecture is suitable for the intended applications.

Resume : In this paper we demonstrate an organic dye nanolaser that exhibits ultrafast modulation speed and high beam directionality [1]. The studied nanolaser consists of arrays of cylindrical gold nanoparticles with a diameter of 100 nm and a height of 30 nm, arranged in a square lattice. The periodicity is varied between 565 – 585 nm. To probe the lasing properties, IR-140 dye (5,5΄-dichloro-11- diphenylamine-3,3΄-diethyl-10,12-ethylene-thiatricarbocyanine-perchlorate), in low concentration solutions is deposited on the sample. In this configuration, the sample exhibit lasing at room temperature at infrared wavelength (~ 880 nm). Similar plasmonic lattices have enable lasing at the visible wavelengths in both bright and dark modes [2]. To gain insight into the temporal lasing dynamics of the sample, we utilize a single-colour pump probe approach where we measure the time-integrated photoluminescence (PL) spectrum for varying delays of the weak probe pulse. This pump-probe approach uses the intrinsic nonlinearity in lasing to examine the lasing dynamics [3]. We optically excite the sample at 45° incident angle with a 34-femtosecond pump at λ = 800 nm. Above the threshold of 120 μW, we see a remarkably rapid modulation speed. By realizing a comprehensive above-threshold power dependence of the temporal characteristics of the samples, we observe a strong dependence of the laser dynamics. References: [1] K.S. Daskalakis et al., manuscript under review (2017). [2] T.K. Hakala, H.T. Rekola, A.I. Väkeväinen, J.-P Martikainen, M. Neĉada, A.J. Moilanen & P. Törmä, Nat. Commun. 8, 13687 (2017). [3] T.P.H. Sidiropoulos, R. Röder, S. Geburt, O. Hess, S.A. Maier, C. Ronning & R.F. Oulton, Nat. Phys. 10, 1038 (2014).

Resume : The success of the silicon-on-insulator platform in photonic integrated circuits (PICs) stems from the high refractive index contrast between a thin waveguide and an optical substrate, enabling to pattern sub-µm, strongly confining structures. However, its application to nonlinear photonics suffers from two-photon absorption (TPA) at 1.55 µm and a weak nonlinearity. AlGaAs, the well-known semiconductor laser material, is a promising candidate for an ideal nonlinear photonics platform, thanks to its large energy gap set by the Al molar fraction so at so avoid TPA at 1550 nm, its huge (2), and its transparency up to the mid-infrared. Until recently, however, an efficient fabrication procedure of monolithic AlGaAs-on-insulator has lacked, and the performances of optical devices resting on a low-index substrate obtained by selective oxidation of AlAs have been limited by the shortcomings of this process at the crystal/oxide interface. Here we illustrate a fabrication method allowing for the monolithic integration of AlGaAs nanostructures on a low-index oxide substrate. This platform requires a far simpler technology than wafer-bonded PICs, and it has recently proved its potential in the domain of nonlinear nanophotonics, with the demonstration of high-efficiency frequency conversion at sub-wavelength scale. These results pave the way towards the realization of nonlinear metasurfaces and point towards the implementation of low-cost AlGaAs nonlinear optical circuits on-chip.