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2019 Fall Meeting



Diamond for Electronic Devices IV

The continued evolution of diamond growth and technology has led to new opportunities in detectors, high power and high voltage electronics, superconductivity and quantum photonics. This has been strongly driven by advances in the growth technology such as high purity and now large area substrates becoming commercially available.


Several topics will be of particular interest at this meeting, although papers on all aspects of diamond technology are welcome. These include diamond for power electronics, diamond nano-electronic devices, diamond for quantum applications and diamond for bio-devices. In all cases, man-made single crystalline diamond is used either as ultra-pure layer or semiconducting by boron and phosphorus doping. The growth and deposition of high quality diamond films will therefore be a subtopic at the symposium. Quantum metrology applications (for example, magnetrometry based on NV centres) is of key interest. Doping of diamond is a key topic using both boron and phosphorus. in case of phosphorus and boron doping. New areas such as the integration of diamond GaN, Wafer bonding to materials will be given close attention.

Hot topics to be covered by the symposium

  • Wafer bonding of diamond to electronic materials
  • Growth of high purity diamond
  • Doping of diamond
  • Polishing and low damage removal of material
  • Biological interaction with diamond surfaces and devices
  • Surface functionalisation
  • Single Photon Sources (NV, SiV etc)
  • Superconductivity and superconducting devices
  • Micro and Nano – Electromechanical Systems
  • Diamond RF and power devices

List of invited speakers:

  • Yamaguchi Takahide (National Institute of Materials Science, Tsukuba, Japan)
    “Field effect transistor based on diamond/h-BN heterostructures”
  • Mete Atature (University of Cambridge, UK)
    “Strain manipulation of SiV colour centers in diamond”
  • Richard Jackman (University College London, UK)
    “Diamond nanowires with ballistic transport and their use for the first diamond FIN-FET technology”
  • Gavin Morley (University of Warwick, UK)
    “Levitated nanodiamonds towards fundamental physics”
  • David Eon (Institut Néel, Grenoble, France)
    “Diamond Schottky diodes parallelization for high current”
  • Thomas Gerrer (Fraunhofer Institute for Applied Research, Germany)
    “Direct bonding of gallium nitride thin-film transistors onto diamond substrates”
  • Anke Krueger (Bavarian University of Würzburg, Germany)
    “Synthesis and in-depth characterization of highly fluorinated diamond surfaces”
  • Lionel Rousseau (ESIEE Paris, France)
    “Full diamond implants, a new approach for chronical in-vivo applications”
  • Tadatomo Suga, Professor Emeritus of The University of Tokyo, Professor at Meisei University, Japan
    “Room Temperature Bonding of GaN to Si and Diamond by means of the Surface Activated Bonding (SAB) Method”
  • Adam Gali, Hungarian Academy of Sciences, Hungary
    “Novel color centers in diamond for communication and sensing
  • Nianjun Yang, Institute of Materials Engineering, University of Siegen, Germany
    “Diamond supercapacitors”

Scientific Committee members:

  • Ken Haenen, Hasselt University, Institute for Materials Research (IMO) & Division IMOMEC, Belgium
  • Paul May, School of Chemistry, University of Bristol, UK
  • Ian W. Boyd, Brunel University, Uxbridge, UK
  • Julien Pernot, Université Grenoble Alpes, France
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Quantum Technologies : Oliver Williams
Authors : Gavin Morley
Affiliations : University of Warwick

Resume : We have begun developing [1-3] an experiment in which a 1 micron diamond containing a nitrogen vacancy (NV) centre would be put into a spatial quantum superposition. This builds on our proposals [4-8] and those of others [9] which could test if there is a macroscopic limit to the quantum superposition principle. Separately, we have shown that laser writing allows NV centres to be created in chosen locations inside of a diamond, deep enough to allow solid immersion lenses to be made around them, and with spin coherence times at least as long as naturally occurring NV [10]. Finally, we are developing a fibre-coupled magnetometer with an NV ensemble towards possible medical applications [11]. [1] A. T. M. A. Rahman et al., Sci. Rep. 6, 21633 (2016). [2] A. T. M. A. Rahman, A. C. Frangeskou, P. F. Barker and G. W. Morley, Rev. Sci. Instrum. 89, 023109 (2018). [3] A. C. Frangeskou et al., NJP 20, 043016 (2018). [4] S. Bose and G. W. Morley, arXiv:1810.07045 (2018). [5] M. Scala et al., PRL 111, 180403 (2013). [6] C. Wan et al., PRL 117, 143003 (2016). [7] S. Bose et al., PRL 119, 240401 (2017). [8] J. S. Pedernales, G. W. Morley and M. B. Plenio, arXiv:1906.00835 (2019). [9] Z.-q. Yin, T. Li, X. Zhang and L. M. Duan, PRA 88, 033614 (2013). [10] C. J. Stephen et al., arXiv:1807.03643 (2018). [11] M. W. Dale and G. W. Morley, arXiv:1705.01994 (2017).

Authors : Mete Atatüre
Affiliations : University of Cambridge, JJ Thomson Ave., Cambridge CB3 0HE, UK

Resume : Optically active spins confined in diamond offer realistic opportunities for realizing stationary and flying qubits within the context of spin-based quantum information science, particularly for distributed quantum network architectures. The nitrogen-vacancy centre is one of the earliest colour centres in diamond to have been studied intensively and it has rightfully been the physical system of choice for many landmark experiments around the broader theme of quantum technologies. Going beyond the proof of concept demonstrators requires addressing a few challenges that come with the nature of these colour centres – their optical quality, in particular. In parallel with the strong effort to overcome such remaining challenges, there is growing interest to seek alternative colour centres with competitive properties. The group 4 colour centres, such as the silicon and tin vacancy centres, are among many which are currently under investigation for this purpose. In this talk, I will provide a brief snapshot of the recent progress and current challenges for coherent control of such colour centres and their promise for feasible spin-photon interfaces.

Authors : Gergő Thiering and Adam Gali
Affiliations : Wigner Research Centre for Physics, Hungarian Academy of Sciences & Department of Atomic Physics, Budapest University of Technology and Economics

Resume : Group-IV -- Vacancy color centers in diamond are fast emerging quantum bits that can be harnessed in quantum communication and sensor applications. It is an immediate quest to understand their magneto-optical properties, in order to select the appropriate qubits for varying needs of particular quantum applications. We performed a systematic study on the magnetooptical properties of Group-IV -- Vacancy color centers, SiV, GeV, SnV and PbV, in diamond by means of cutting-edge ab initio density functional theory calculations. We identified the photostability of these centers that can act as solid state qubits. We developed a novel spin Hamiltonian for these qubits in which the electron angular momentum and spin as well as the phonons are strongly coupled and identified such terms that have not been considered so far but are important in understanding their magneto-optical properties. We solved ab initio this complex problem for the model of these color centers consisting of up to 1000-atom supercells, and were able to reproduce previous experimental data. We identify SnV(-) and PbV(-) qubits with long spin coherence time at cryogenic temperatures where the spin state of PbV(-) can also be thermally initialized at these temperatures. We predict the magneto-optical properties of the neutral color centers too which are favorable candidates for quantum communication applications.

15:30 Coffee break    
Thermal Management of Semiconductor Devices with Diamond : Richard Jackman
Authors : Tadatomo Suga, Fengwen Mu
Affiliations : Meisei University, Tokyo

Resume : Room temperature bonding of GaN-Si and diamond were achieved by the Surface Activated Bonding (SAB) method. Both of the structure and composition of the bonding interfaces were investigated to understand the bonding mechanisms. The results show that SAB method has a great potential for the integration of GaN onto diamond substrates of a high thermal conductivity. The integration of GaN device such as HEMT onto substrates of high thermal conductivity is a promising approach to enhance the heat dissipation for high power devices. Diamond is expected to be the most ideal material for such substrate of high thermal conductivity. However GaN is not grown directly on diamond. The most approaches so far investigated require certain dielectric layer and nucleation layer of low thermal conductivity or thermal expansion mismatch. Direct bonding of GaN to diamond could overcome all problems face in the diamond growth. There have been several approaches to bond GaN to diampond. However, conventional bonding method, typically solid state boding or the hydrophilic bonding method, use high temperature reaction, resulting in damages and reaction produces of high thermal conductivity at the bonded interfaces. In this work, we proposed to employ the modified surface-activated- bonding (SAB) method to bond GaN to diamond at room temperature. GaN and Si were also bonded intend to investigate and understand the bonding mechanism. The bonding process is carried out in a vacuum system, in which the material surfaces are irradiated by Ar ion beam bombardment to be activated for bonding. In the modified SAB, the activation process is combined with simultaneous deposition of Si, metals, or certain oxides. Then the activated surfaces are brought into contact at room temperature under a pressure or without pressure depending on the conditions. A polycrystalline diamond film on Si was bought for bonding demonstration. The thickness of the diamond film is ~900 nm and the size of the diamond sample is 1 cm × 1 cm. The diamond surface has already been carefully smoothed by polishing. An as-grown GaN template, which is ~2 μm thick GaN epitaxial layer grown on a ~430 μm thick sapphire substrate, was used for the experiments. The average root-mean-square (RMS) surface roughness of GaN surface and diamond surface was ~0.4 nm and ~1.0 nm, respectively. GaN-diamond was bonded well with a uniform interface structure with three intermediate layers: two amorphous Si layer with a thickness of ~12 nm and an amorphous-like diamond layer of ~3 nm thickness which could be caused by ion beam bombardment. Based on the micro-structure observations by STEM and the analysis of EDX mapping, a transition layer exists between diamond and the deposited Si layer as well as between the deposited Si layer and GaN, which should be caused by the sputtering deposition of the Si nano-layer. Further study on GaN-diamond bonding using an even thinner Si nano-layer as well as measurements of thermal resistance of the bonding interface will be conducted. This work is expected to be helpful for the applications of high-power GaN devices. As the summary, a uniform GaN-on-diamond structure was successfully fabricated by the bonding of GaN to diamond at room temperature by using our modified SAB method. ACKNOWLEDGMENT This research was conducted under a contract of R&D for Expansion of Radio Wave Resources, organized by the Ministry of Internal Affairs and Communications, Japan.

Authors : Thomas Gerrer, Heiko Czap, Thomas Maier, Fouad Benkhelifa, Stefan Müller, Christoph Nebel, Patrick Waltereit, Rüdiger Quay, Volker Cimalla
Affiliations : Fraunhofer Institute for Applied Solid State Physics

Resume : Several semiconductor applications like LEDs, acoustic filters, sensors, solar cells, microwave amplifiers, and power converters are based on III-nitrides like AlN, GaN and InN as well as ternary and quaternary III-nitride based alloys. These materials are grown economically and with high crystalline quality as several micron thick layers on foreign substrates like sapphire, silicon and silicon carbide. The transfer of semiconductor devices based on such thin films onto diamond as new substrate promises to improve the performance of such devices. Therefore, such transfer technologies are investigated by several groups. In this talk, we present a direct bond technique, which transforms the surface of the thin-film nucleation layer into a solid bond layer. This chemical process is based on the dissolution of and recrystallization of aluminum compounds within several nanometers of interfacial water, thereby restructuring and adapting the interfaces to form a homogeneous bond contact without any interfacial voids. With this technology we demonstrate AlGaN/GaN microwave transistors on diamond with excellent electro-thermal performance. The combined qualities of our bond layer being thin, electrically insulating, mechanically hard and optically transparent make this technology interesting for several other III-nitride applications.

Authors : Soumen Mandal1*, Jerome A. Cuenca1, Henry Bland1, Chao Yuan2, Fabien Massabuau3, James W. Pomeroy2, David Wallis3,4, Rachel Oliver3, Martin Kuball2, Oliver A. Williams1
Affiliations : 1School of Physics and Astronomy, Cardiff University, Cardiff, UK 2Center for Device Thermography and Reliability, Bristol University, Bristol, UK 3Department of Materials Science & Metallurgy, University of Cambridge, Cambridge, UK 4School of Engineering, Cardiff University, Cardiff, UK,

Resume : Inefficient heat extraction in high power and high frequency devices is a major obstacle towards full utilisation of materials like GaN. The current technique of using SiC substrate has allowed good device performances, but it still cannot harness the full potential of high power materials. Replacing SiC(kSiC ~ 360 – 490 W/m K) with diamond(kDiamond ~ 2100 W/m K) is a very good option. For diamond to be used for thermal management it is important that the diamond layer is at least 50-100 microns thick1. While the growth of thin diamond layer on GaN is possible2, growing a 100 micron thick layer is non-trivial. This is due to absence of any covalent bond between diamond and the GaN layer. Hence, the growth of a thick diamond layer on GaN can only be achieved by a suitable intermediate layer. In the literature there are studies where SiNx layers have been used but they have shown high thermal barrier resistance. Alternatively, AlN can be used for such thick diamond growth. AlN is also the seed layer for growth of GaN on silicon. As a result no extra seed layer needs to be deposited after flipping the GaN film onto a suitable carrier. In this work we demonstrate the growth of >100 micron thick diamond layer on AlN. We have measured the zeta potential of the AlN surface. The zeta potential was found to be negative but still we found that both H-terminated (positively charged) and O-terminated (negatively charged) seeds had resulted in a good diamond layer. For growth of diamond with O-terminated seeds the surface was pre-treated with a H2/N2 gas mix plasma. X-ray photo luminescence spectroscopy on the treated substrates revealed an increase in oxygen content on the surface after plasma treatment. This could be due to removal of surface nitrogen from the substrates and oxygenation of the aluminium bonds on subsequent exposure to air and seed solution. Cross-sectional studies of the films showed larger grains at the interface with a small number of voids in the films grown with O-terminated seeds. The voids are likely to relax the stress in the film caused due to unmatched thermal expansion coefficient of AlN and diamond. The growth of diamond on AlN seeded with H-terminated seeds resulted in good quality films as expected. Thermal barrier resistance between the diamond and AlN layer was also studied and low thermal barrier resistance was confirmed for films grown with O-terminated seeds. The study has clearly shown that even though H-terminated seeds are needed for high seed density on AlN surface, O-termiated seeds can be used to grow thick diamond films with large grains at the diamond-AlN interface. References 1 Y. Zhou, R. Ramaneti, J. Anaya, S. Korneychuk, J. Derluyn, H. Sun, J. Pomeroy, J. Verbeeck, K. Haenen, and M. Kuball, Appl. Phys. Lett. 111, (2017). 2 S. Mandal, E.L.H. Thomas, C. Middleton, L. Gines, J.T. Griffiths, M.J. Kappers, R.A. Oliver, D.J. Wallis, L.E. Goff, S.A. Lynch, M. Kuball, and O.A. Williams, ACS Omega 2, 7275 (2017).

Authors : Jae-Kap Lee
Affiliations : Center for Opto-electronic Materials and Devices, Korea Institute of Science and Technology (KIST), Seoul 02792, South Korea.

Resume : Due to the eminent physical properties of diamond, its successful synthesis by chemical vapor deposition (CVD) in 1980?s [1] has excited the scientists who study next-generation electronics. Diamond is the ultimate material not only as active devices [2], but also thermal spreaders for high power electronics. Recently, GaN-diamond high electron mobility transistor (HEMT) devices [3], where diamond is in charge of heat dissipation, become the issue for high power next-generation electronic devices. In this talk, I introduce multi (7)-cathode direct current plasma assisted CVD (MCDC PACVD) system for synthesis of 4? diamond wafers of ~1 mm in thickness [4] and its performance to deposit diamond as well as diamond-based carbon hybrid structures. We also introduce recent studies in KIST for diamond electronics, including single-crystal diamond growth, bandgap engineering of diamond [5] as well as diamond engineering for HEMT application (i.e., thermal managements). References 1. J. E. Butler & R. L. Woodin, Thin film diamond growth mechanisms. Phil. Trans. R. Soc. Lond. A 342, 209-224 (1993). 2. C. J. H. Wort, & R.S. Balmer, Diamond as an electronic material. Materials Today 11, 22-28 (2008). 3. G. H. Jessen et al., AlGaN/GaN HEMT on diamond technology demonstration. Proc. IEEE Compound Semiconductor Integr. Circuit Symp., pp 271-274 (2016). 4. Lee, J.-K. et al. The large area deposition of diamond by the multi-cathode direct current plasma assisted chemical vapor deposition (DC PACVD) method. Diamond and Related Materials 11, 463-466 (2002). 5. Lee, J.-K. et al. A route to bandgap engineering of diamond, submitted.

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Diamond Electronic Devices I : Gauthier Chicot
Authors : David EON
Affiliations : Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France

Resume : The Schottky diodes will be the first components commercially available for the diamond technology. However, we have to manage the surface defects which is still too high for large contact, with the current requirement and the rectification behavior. Even though a number of studies have already been performed, some questions are still without answer. One of them is how is the electric field into the stack of diamond layer. From the theory and by doing simulation we know how it should be but experimentally we are able to see only the lateral electric field distribution by performing electron beam induced current (EBIC) and that gives us only a partial view of the problem and not the entire picture The second major problem is the study of the interface and the identification of defects that could lead to a modification of the Schottky barrier. With this study, we propose a new approach combining growth technic and electrical characterization in order to see what is happening underneath the Schottky contact in the depth of the material. The first part was to grow and fabricate the stack for diamond Schottky diode i.e heavily doped p++ layer on top of an HPHT substrate. And after a thick non intentionally doped layer (p-) was grown. Once the sample ready, polishing was performed to remove the lateral overgrowth. Thus, the stack was directly accessible to different electronic probes. We performed EBIC and cathodoluminescence measurements. For instance, For example, with EBIC we observed the electric field directly under the contact for different polarization of the diode. Following this, we combined cathodoluminescence measurements with a specific mapping underneath the contact to correlate the presence of defects and the intensity of EBIC signals which is related to barrier inhomogeneities.

Authors : T. Hanada, H. Umezawa, S. Ohmagari, H. Kawashima, D. Takeuchi, J. Kaneko
Affiliations : Hokkaido University; AIST

Resume : Diamond is attracting attentions for future semiconductor devices such as high power and low loss devices worked under harsh environmental conditions. High current capability > 3kA/cm2 with long-term stability at high temperature condition > 400degC has been confirmed on SBDs. High radiation hardness of SBDs and MESFETs after 10 MGy of X/gamma-ray has been confirmed as well. Typical maximum electric field strength of the devices are more than 2MV/cm, however, it decreases with increasing the size of the main contact. Estimated density of the defect was in the order of 10,000 /cm2 by Murphy’s analysis and the origin of the defect was not clarified up to now. In this study, diamond SBDs have been fabricated on 0.5 inch wafer by minimal fab system and the yield of the device is analyzed to understand the origin of the defects. Diamond SBDs with pseudo-vertical structure were fabricated on a CVD grown nitrogen doped semi-insulating (001) substrate. p-/p+ Stacked film was deposited by microwave plasma and hot filament CVD techniques. Ohmic and Schottky contacts were fabricated on the same side of the substrate. To suppress the field enhancement at the edge of the main contact, SiO2 field-plate was utilized. The diameter/length of the main contact was varied from 25 to 700 µm. The fabricated SBDs show high on/off ratio when the size of the main contact is less than 220µm, however, the high leakage devices are confirmed with size increased. The estimated density of the defects by Murphy’s analysis is 100 /cm2 which is, at least, two orders of magnitude less than that of crystallographic defect in the substrate. From this analysis, the main reasons of the low yield of diamond devices is the defects during the device processing rather than the crystallographic defects in the film/substrate.

Authors : Abdulkareem Afandi1, Alexander C. Pakpour-Tabrizi1, Evgeny Ekimov2, Igor Vlasov3, Nicholas Nunn4, Olga Shenderova4, Joseph O. Welch1, Richard B. Jackman1,
Affiliations : 1 London Centre for Nanotechnology and Department of Electronic and Electrical Engineering, University College London (UCL), 17-19 Gordon Street, London, WC1H 0AH, UK 2 Institute for High Pressure Physics, RAS, Kaluzhskoe Road 14, Troitsk, Moscow 142190, Russia 3 General Physics Institute, RAS, Vavilov Street 38, 119991 Moscow, Russia 4 Adámas Nanotechnologies, Inc., 8100 Brownleigh Drive, S.120, Raleigh, NC 27617, USA

Resume : Nanodiamonds (NDs) are a readily sourced and relatively inexpensive materials. Here, it has been shown that for boron-doped NDs the nano-size of such particles enable them to act as a source of boron dopant when subsequent plasma-CVD diamond growth is carried out on them, without the need for the addition of B-containing species to the plasma-CVD feedstock gases. Here the potential use of B-NDs for the formation of diamond Schottky Diodes through such an approach is explored. Two types of B-NDs are studied; those produced by a top-down process of milling B-doped diamond films and others produced by a bottom-up chemical synthesis approach. In all cases effective diodes were produced with barrier heights of 0.6-0.7eV. Early indications are that the bottom-up grown NDs may offer better breakdown voltages when using this approach, potentially because of their smaller size (~10nm).

Authors : Yamaguchi Takahide
Affiliations : National Institute for Materials Science, Japan

Resume : In this talk, I will present the fabrication and characterization of diamond field effect transistors (FETs) with a monocrystalline hexagonal boron nitride (h-BN) as a gate dielectric. A thin crystal of h-BN was obtained by using the Scotch tape exfoliation technique and laminated on hydrogen-terminated (111) diamond surface. A high-quality interface between h-BN and diamond was confirmed by transmission electron microscopy. Excellent insulating properties of h-BN led to high carrier mobilities and low on-resistance of the FETs. The high mobility allowed us to observe quantum oscillations, which provided important information on the hole gas accumulating at the diamond surface. The heterostructure consisting of monocrystalline h-BN and hydrogen-terminated diamond will provide an excellent platform for the study of quantum transport in diamond, as well as the fabrication of high-performance electronic devices. Reference: Y. Sasama et al. APL Materials 6, 111105 (2018).

10:30 Coffee break    
Diamond Electronic Devices II : Hitoshi Umezawa
Authors : Alexander C Pakpour-Tabrizi, Richard B. Jackman
Affiliations : London Centre for Nanotechnology and Department of Electronic and Electrical Engineering, University College London (UCL), 17-19 Gordon Street, London WC1H 0AH, UK

Resume : Semiconductor nanowires (NWs) represent one of the most important and versatile nanometre-scale structures. In contrast to other classes of 1D nanostructures, such as carbon nanotubes, semiconductor NWs can be rationally and predictably synthesized in single crystal forms with all key parameters controlled, including chemical composition, diameter, length, doping and electronic properties. Diamond can be considered as an ultimate semiconductor with a band-gap of 5.5eV and outstanding electrical properties. We report novel nanoscale electrically addressable diamond nanowire devices. Based on extremely high-quality boron-doped diamond delta-layers, this technology provides an exciting playground for exotic physics and traditional electronic engineering, and many applications in sensor technology. Lateral nanowires are defined in very thin heavily boron doped diamond epi layers. In the results reported here, the delta layer is on the surface of a [100] single crystal diamond. Electrical isolation is possible due to the very low defect and high quality ‘intrinsic’ CVD buffer layer grown on the HPHT substrate before the ∂-layer is grown. The resultant nanowires are some 2nm deep and 10-20nm wide, and show current densities surpassing 300A/mm2. After etching the nanowires the spatial confinement and electrical properties of the wire can be further engineered using electrostatic side and top gating. We report exceptional current densities indicative of ballistic transport and preliminary results from the first ever fabricated diamond-FinFET type devices; an architecture used in the silicon industry for the next generation of processor chips, but obviously without the extreme transport properties shown here. Further, the prospects for the use of these nanowires as sensors for the trace detection of a range important species will be considered.

Authors : C. Schreyvogel1, V. Zuerbig1, J. Langer1, C. Giese1, V. Cimalla1, S. Temgoua2, J. Barjon2 and C.E. Nebel1
Affiliations : 1 Fraunhofer-Institute for Applied Solid State Physics (IAF), Tullastr. 72, 79108 Freiburg, Germany 2 Groupe d'Etude de la Matière Condensée (GEMAC), Université Saint-Quentin en Yvelines, 45 Avenue des Etats-Unis,78000, Versailles, France

Resume : Fabrication of diamond power devices as prototypes can be based on structures with stacked layers consisting of buried epitaxial layers or buried wells. To fabricate buried n-doped wells for example, the technology involves several steps such as realization of V-shape structures via catalytic etching with nickel along defined crystalline directions of the diamond layer and subsequent growth of n-doped layer via phosphorous doping. In this paper we report first on experimental results of phosphorous doping at different growth conditions to pave the way for finding optimum growth conditions leading to high phosphorous incorporation, suppression of nitrogen incorporation and low growth rates required for fabricating thin, high quality n-type layers. Then we go on with catalytic etching on intrinsic (100) diamond via nickel. Catalytic etching on (100) diamond layers results in V-shapes with atomically smooth (111)-oriented sidewalls and (100)-oriented bottoms, whereas the crystalline orientation of the sidewalls is optimal for the growth of n-type doped layers since in these layers the incorporation efficiency of phosphorous is higher enabling realization of highly doped n-type layers in (100) diamond. Experimental results indicate for example that the relationship between the orientation of the nickel mask and the crystal orientation of the diamond layer is important. Smooth (111) etched surfaces are achieved by depositing the nickel mask with edges parallel to the <110> direction of the diamond layer. The fabricated V-shape structures are subsequently overgrown with n-type layers. CL measurements on these grown n-type wells reveal different degree of phosphorous incorporation for different crystal orientation of the facets.

Authors : J. A. Durk (1,2), B.P. Reed (1,2,3), S.P. Cooil (1,4), D. Hu (1), A. Can (5), M. Motchelaho (5), D.A. Evans (1)
Affiliations : (1) Department of Physics, Aberystwyth University, UK ; (2) EPSRC Centre for Doctoral Training in Diamond Science and Technology, UK ; (3) National Physical Laboratory, UK ; (4) Department of Physics, NTNU, Trondheim, Norway ; (5) Element Six Ltd, UK

Resume : There is considerable interest in the fabrication and electronic properties of graphene and related 2D materials, such as hexagonal boron nitride (hBN), for low-dimensional materials engineering. [1] Previously, catalytic conversion of diamond substrates into large-domain high-quality graphene was shown, via transition-metal-induced growth of sp2 bonded carbon from sp3 bonded surface atoms. [2] Modern advancements in sintering of polycrystalline cubic boron nitride have made possible comparative methodology for mediated growth of low-dimensional hBN regions. In-situ deposition and annealing cycles were performed, and through use of real-time photoelectron-based methods, the proliferation of BN through a metallic overlayer was observed with temperature dependence. Boron and nitrogen K-edge spectra of the near-edge X-ray absorption fine structure (NEXAFS) allowed for clear determination of hexagonal phase, due to the emergent π-π* transition state not present in the cubic phase. [3] The results indicate that controllable growth of single and multi-layer hBN is feasible, given precise control over substrate temperature, polish and pre-treatment. This technique may provide a new alternative source of high-quality low-dimensional hBN for graphene-based electronic devices with wide band gap substrates. [1] C. R. Dean et al., Nat. Nanotechnol., 5, 10, 722, (2010). [2] S. P. Cooil et al., Appl. Phys.Lett., 107, 18, (2015). [3] D. A. Evans et al., Appl. Phys. Lett., 89, 161107 (2006).

Authors : Jeroen Prooth, Milos Nesladek, Hans-Gerd Boyen
Affiliations : Materials Research Institute, Hasselt University, Wetenschapspark 1, Diepenbeek, Belgium, Materials Research Institute, Hasselt University, Wetenschapspark 1, Diepenbeek, Belgium, Materials Research Institute, Hasselt University, Wetenschapspark 1, Diepenbeek, Belgium

Resume : Controlled synthesis of nanodiamond particles has recently seen an increased interest due to breakthroughs in quantum sensing and entanglement, biolabeling, and nanoscale sensing[1]. While nanodiamonds are typically fabricated in large amounts by two main techniques: (1) detonation synthesis and (2) by crushing larger microsized crystals[2], neither of these methods allow for a high degree of manipulation of their properties. High quality nanodiamonds grown by chemical vapour deposition are thus highly favoured for precise control over crystal morphology, size, and dopants. Since nucleation and early stages of growth play an important role in the properties of the particles[3], it is mandatory to reach equilibrium within the plasma conditions as quickly as possible so that nucleation happens at equivalent parameters. Here we propose a methane pulsing scheme to quickly increase methane concentration, allowing it to reach steady-state concentration within seconds instead of minutes depending on pressure, chamber volume, target concentration, and attainable flows. Pulses are designed by numerical simulations and compared to experiments performed by optical emission spectroscopy for accuracy. The influence of the pulsing schemes on diamond growth is studied by growing on vertically aligned substrates, allowing to rapidly explore the effect on a broad parameter space, since temperature, plasma density and hydrogen density vary continuously along the vertical axis[1]. The developed technique allows us to prepare ND with nearly perfect crystalline shape of size < 100 nm and various type of colour centres as characterised spectrally. We also present data on coherence time in NV nanodiamonds and compare with HPHT nanocrystals. References: 1. Tzeng, Y., Zhang, J., et al. (2017). Vertical-Substrate MPCVD Epitaxial Nanodiamond Growth. Nano Letters, 17 (3), pp. 1489-1495. 2. Alkahtani, M., Alghannam, F., Jiang, L., et al. (2018). Fluorescent nanodiamonds: past, present, and future. Nanophotonics, 7(8), pp. 1423-1453. 3. Domonkos, M., Ižák, T., et al. (2018), Diamond nucleation and growth on horizontally and vertically aligned Si substrates at low pressure in a linear antenna microwave plasma system. Diamond and Related Materials, 82, pp. 41-49.

Authors : J Ash [1,2], S. P. Cooil [1,3], D. Hu [1] and D.A. Evans [1]
Affiliations : [1] Department of Physics, Aberystwyth University, Wales, [2] EPSRC Centre for Doctoral Training in Diamond Science and Technology, UK, [3] Department of Physics, Norwegian University of Science and Technology, Norway

Resume : The negatively charged Nitrogen Vacancy (NV-) centre in diamond has been shown to possess desirable properties for use in quant