87 research outputs found
Spatially-Correlated Microstructure and Superconductivity in Polycrystalline Boron-Doped Diamond
Scanning tunneling spectroscopies are performed below 100~mK on
nano-crystalline boron-doped diamond films characterized by Transmission
Electron Microscopy and transport measurements. We demonstrate a strong
correlation between the local superconductivity strength and the granular
structure of the films. The study of the spectral shape, amplitude and
temperature dependence of the superconductivity gap enables us to differentiate
intrinsically superconducting grains that follow the BCS model, from grains
showing a different behavior involving the superconducting proximity effect
Spectroscopic ellipsometry of homoepitaxial diamond multilayers and delta-doped structures
5 pagesInternational audienceThe optimization of diamond-based unipolar electronic devices such as pseudo-vertical Schottky diodes or delta-doped field effect transistors relies in part on the sequential growth of nominally undoped (p-) and heavily boron doped (p þþ ) layers with well-controlled thicknesses and steep interfaces. Optical ellipsometry offers a swift and contactless method to characterize the thickness, roughness, and electronic properties of semiconducting and metallic diamond layers. We report ellipsometric studies carried out on delta-doped structures and other epitaxial multilayers with various boron concentrations and thicknesses (down to the nanometer range). The results are compared with Secondary Ion Mass Spectroscopy and transport measurements. Copyright 2014 AIP Publishing LLC
Non-adiabatic Kohn Anomaly in Heavily Boron-doped Diamond
We report evidence of a non-adiabatic Kohn anomaly in boron-doped diamond,
using a joint theoretical and experimental analysis of the phonon dispersion
relations. We demonstrate that standard calculations of phonons using density
functional perturbation theory are unable to reproduce the dispersion relations
of the high-energy phonons measured by high-resolution inelastic x-ray
scattering. On the contrary, by taking into account non-adiabatic effects
within a many-body field-theoretic framework, we obtain excellent agreement
with our experimental data. This result indicates a breakdown of the
Born-Oppenheimer approximation in the phonon dispersion relations of
boron-doped diamond.Comment: 6 pages, 2 figure
TEM study of homoepitaxial diamond layers scheduled for high power devices: FIB method of sample preparation
Homoepitaxial diamond structure observation by transmission electron microscopy (TEM) is still a very hard job due to the difficulty in preparing electron transparent samples for the further observation. The present contribution details the experimental operations with their respective conditions step by step. Finally high resolution TEM (HREM) observations of a CVD grown epilayer on a unnintentionally doped HPHT (001) oriented substrate are present to show the high quality of the sample preparation method.4 page
Dependence of the superconducting transition temperature on the doping level in single crystalline diamond films.
Homoepitaxial diamond layers doped with boron in the 10^20-10^21 /cm3 range are shown to be type II superconductors with sharp transitions (~0.2K) at temperatures increasing from 0 to 2.1 K with boron contents. The critical concentration for the onset of superconductivity is about 5-7 10^20 /cm3, close to the metal-insulator transition. The H-T phase diagram has been obtained from transport and a.c. susceptibility measurements down to 300mK. These results bring new quantitative constraints on the theoretical models proposed for superconductivity in diamond
Superconducting group-IV semiconductors
International audienceWe present recent achievements and predictions in the field of doping-induced superconductivity in column IV-based covalent semiconductors, with a focus on Bdoped diamond and silicon. Despite the amount of experimental and theoretical work produced over the last four years, many open questions and puzzling results remain to be clarified. The nature of the coupling (electronic correlation and/or phonon-mediated), the relationship between the doping concentration and the critical temperature (TC), which determines the prospects for higher transition temperatures, as well as the influence of disorder and dopant homogeneity, are debated issues that will determine the future of the field. We suggest that innovative superconducting devices, combining specific properties of diamond or silicon, and the maturity of semiconductor-based technologies, will soon be developed
Boron concentration profiling by high angle annular dark field-scanning transmission electron microscopy in homoepitaxial delta-doped diamond layers
To develop further diamond related devices, the concentration and spatial location of dopants should be controlled down to the nanometer scale. Scanning transmission electron microscopy using the high angle annular dark field mode is shown to be sensitive to boron doping in diamond epilayers. An analytical procedure is described, whereby local boron concentrations above 1020 cm-3 were quantitatively derived down to nanometer resolution from the signal dependence on thickness and
boron content. Experimental boron local doping profiles measured on diamond p-/p++/p- multilayers are compared to macroscopic profiles obtained by secondary ion mass spectrometry, avoiding reported artefacts.4 page
Boron-doped superlattices and Bragg mirrors in diamond
International audienceA periodic modulation of the boron doping level of single crystal diamond multilayers over more than three orders of magnitude during epitaxial growth by microwave plasma-enhanced chemical vapor deposition is shown to yield Bragg mirrors in the visible. The thicknesses and doping level of the individual layers were controlled by in situ spectroscopic ellipsometry, enabling to tune the reflec-tance peak to the wavelength range of diamond color centers, such as NV 0 or NV À . The crystalline quality, periodicity, and sharpness of the doping transitions in these doping superlattices over tens of periods were confirmed by high resolution X-ray diffraction
Doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide
International audienceWe report an experimental determination of the doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide. Low temperature transport measurements down to 360 mK and temperature dependent Raman experiments down to 5 K, together with secondary ion mass spectroscopy profiling, suggest a critical aluminum concentration lying between 6.4 and 8.7 1020 cm−3 for the metal-insulator transition in these epilayers grown by the vapor-liquid-solid technique. Preliminary indications of a superconducting transition in the metallic sample are presented
Strain relaxation in GaN grown on vicinal 4H-SiC(0001) substrates
The strain of GaN layers grown by Metal Organic Chemical Vapor Deposition
(MOCVD) on three vicinal 4H-SiC substrates (0, 3.4 and 8 offcut from [0001]
towards [11-20] axis) is investigated by X-ray Diffraction (XRD), Raman
Scattering and Cathodoluminescence (CL). The strain relaxation mechanisms are
analyzed for each miscut angle. At a microscopic scale, the GaN layer grown on
on-axis substrate has a slight and homogeneous tensile in-plane stress due to a
uniform distribution of threading dislocations over the whole surface. The GaN
layers grown on miscut substrates presented cracks, separating areas which have
a stronger tensile in-plane stress but a more elastic strain. The plastic
relaxation mechanisms involved in these layers are attributed to the step flow
growth on misoriented surfaces (dislocations and stacking faults) and to the
macroscopical plastic release of additional thermoelastic stress upon cooling
down (cracks)
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