Heavily boron doped diamond epilayers with thicknesses ranging from 40 to less than 2 nm and buried between nominally undoped thicker layers have been grown in two different reactors. Two types of [100]-oriented single crystal diamond substrates were used after being characterized by X-ray white beam topography. The chemical composition and thickness of these so-called delta-doped structures have been studied by secondary ion mass spectrometry, transmission electron microscopy, and spectroscopic ellipsometry. Temperature-dependent Hall effect and four probe resistivity measurements have been performed on mesa-patterned Hall bars. The temperature dependence of the hole sheet carrier density and mobility has been investigated over a broad temperature range (6 K < T < 450 K). Depending on the sample, metallic or non-metallic behavior was observed. A hopping conduction mechanism with an anomalous hopping exponent was detected in the non-metallic samples. All metallic delta-doped layers exhibited the same mobility value, around 3.6 ± 0.8 cm2/Vs, independently of the layer thickness and the substrate type. Comparison with previously published data and theoretical calculations showed that scattering by ionized impurities explained only partially this low common value. None of the delta-layers showed any sign of confinement-induced mobility enhancement, even for thicknesses lower than 2 nm

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Scanning tunneling spectroscopies are performed below 100 mK on polycrystalline 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. DOI: 10.1103/PhysRevB.82.033306 PACS number͑s͒: 73.22.Ϫf, 73.61.Cw, 74.45.ϩc, 74.81.Bd Over the last few years, superconductivity has been discovered in heavily doped group IV covalent semiconductors, 1 in particular, diamond 2 and silicon. 3 In the case of diamond, low-temperature superconductivity appears at the same doping level than the metallic state created by heavy boron doping. 4 Evidence for a pairing mechanism mediated by phonons in the weak-coupling limit has been provided among others by very low-temperature scanning tunneling spectroscopy of single-crystal epilayers. 5Polycrystalline diamond films can be a new model system for the general issue of the nature of superconductivity in strongly disordered metals. 6 In such systems, disorder sits either at the atomic scale, in which case electronic excitations can become localized so that superconductivity vanishes 7 or at a larger scale, for instance, that of a granular structure, in which case the two competing mechanisms are the Coulomb blockade and the superconducting proximity effect. 8,9 Nevertheless, recent studies of polycrystalline diamond films 10,11 did not provide a clear picture on the coexistence between superconductivity and disorder in these films.In this Brief Report, we report a study of the local superconducting and structural properties of high-quality polycrystalline boron-doped diamond by very low-temperature scanning tunneling microscopy ͑STM͒. The granular structure was consistently characterized by STM and transmission electron microscopy ͑TEM͒. In contrast with epitaxial films, a strong correlation is observed between the granular microstructure and the superconductivity local strength. The spatial evolution and temperature dependence of the local electronic density of states are consistent with the picture of an assembly of grains, which either follow the BCS model or present another superconducting behavior involving the superconducting proximity effect.Boron-doped polycrystalline diamond thin films of different thicknesses were grown as described elsewhere 12,13 by microwave plasma-enhanced chemical-vapor deposition from hydrogen-rich methane-trimethylborane-hydrogen gaseous mixtures on ultrasonically seeded quartz ͑sample A͒ and oxidized silicon ͑sample B͒ substrates. As shown by Figs. 1͑a͒ and 1͑b͒ displaying, respectively, a very lowtemperature STM ͑Refs. 14 and 15͒ topography of sample A and a TEM cross section in bright-field condition of sa...

International audienceDefects induced by boron doping in diamond layers were studied by transmission electron microscopy. The existence of a critical boron doping level above which defects are generated is reported. This level is found to be dependent on the CH 4 /H 2 molar ratios and on growth directions. The critical boron concentration lied in the 6.5–17.0 10 20 at/cm 3 range in the <111> direction and at 3.2 10 21 at/cm 3 for the <001> one. Strain related effects induced by the doping are shown not to be responsible. From the location of dislocations and their Burger vectors, a model is proposed, together with their generation mechanism

AIN/diamond heterostructures are very promising for high frequency surface acoustic wave (SAW) resonators. In their design, the thickness of the piezoelectric film is one of the key parameters. On the other hand, the film material quality and, hence, the device performance, also depend on that thickness. In this work, polished microcrystalline diamond substrates have been used to deposit AIN films by reactive sputtering, from 150 nm up to 3 um thick. A high degree of the c-axis orientation has been obtained in all cases. SAW one port resonators at high frequency have been fabricated on these films with a proper combination of the film thickness and transducer size.

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InN quantum dots (QDs) on GaN (0001) grown by metalorganic vapor phase epitaxy onto a sapphire substrate were studied by transmission electron microscopy (TEM). We found that the nucleation of InN QDs on GaN is directly related to the presence of threading dislocations (TDs) in the center of the QDs. The TEM analysis revealed that the TDs finish at the InN∕GaN interface and they are pure edge dislocations. Therefore, spiral growth models cannot explain nucleation of these QDs. Although controlling edge TDs constitute a possible approach to determine the QD density, a better approach may be an increase in the material growth rate in order to enter the diffusion-limited growth mode, where growth is not sensitive to surface heterogeneities.