113 research outputs found
Superconductivity in doped semiconductors
International audienceA historical survey of the main normal and superconducting state properties of several semiconductors doped into superconductivity is proposed. This class of materials includes selenides, tellurides, oxides and column-IV semiconductors. Most of the experimental data point to a weak coupling pairing mechanism, probably phonon-mediated in the case of diamond, but probably not in the case of strontium titanate, these being the most intensively studied materials over the last decade. Despite promising theoretical predictions based on a conventional mechanism, the occurrence of critical temperatures significantly higher than 10 K has not been yet verified. However, the class provides an enticing playground for testing theories and devices alike
Tunneling Spectroscopy and Vortex Imaging in Boron-Doped Diamond
We present the first scanning tunneling spectroscopy study of
single-crystalline boron doped diamond. The measurements were performed below
100 mK with a low temperature scanning tunneling microscope. The tunneling
density of states displays a clear superconducting gap. The temperature
evolution of the order parameter follows the weak coupling BCS law with
. Vortex imaging at low magnetic field also
reveals localized states inside the vortex core that are unexpected for such a
dirty superconductor.Comment: 4 pages, 4 figures, replaced with revised versio
Superconducting and Normal State Properties of Heavily Hole-Doped Diamond
We report measurements of the specific heat, Hall effect, upper critical
field and resistivity on bulk, B-doped diamond prepared by reacting amorphous B
and graphite under high-pressure/high-temperature conditions. These experiments
establish unambiguous evidence for bulk superconductivity and provide a
consistent set of materials parameters that favor a conventional, weak coupling
electron-phonon interpretation of the superconducting mechanism at high hole
doping.Comment: 10 pages, 3 figure
Absence of boron aggregates in superconducting silicon confirmed by atom probe tomography
Superconducting boron-doped silicon films prepared by gas immersion laser
doping (GILD) technique are analyzed by atom probe tomography. The resulting
three-dimensional chemical composition reveals that boron atoms are
incorporated into crystalline silicon in the atomic percent concentration
range, well above their solubility limit, without creating clusters or
precipitates at the atomic scale. The boron spatial distribution is found to be
compatible with local density of states measurements performed by scanning
tunneling spectroscopy. These results, combined with the observations of very
low impurity level and of a sharp two-dimensional interface between doped and
undoped regions show, that the Si:B material obtained by GILD is a well-defined
random substitutional alloy endowed with promising superconducting properties.Comment: 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
Phase diagram of boron-doped diamond revisited by thickness-dependent transport studies
International audienceWe report on a detailed study of the electronic properties of a series of boron-doped diamond epilayers with dopant concentrations ranging from 1.10^ 20 to 3.10^21 cm −3 and thicknesses (d ⊥) ranging from 2 µm to 8 nm. By using well-defined mesa patterns that minimize the parasitic currents induced by doping inhomogeneities, we have been able to unveil a new phase diagram differing from all previous reports. We show that the onset of superconductivity does actually not coincide with the metal-insulator transition in this system. Moreover a dimensional crossover from 3D to 2D transport properties could be induced by reducing d ⊥ in both the metallic non-superconducting and superconducting epilayers, without any reduction of Tc with d ⊥ in the latter
High Field magnetospectroscopy to probe the 1.4eV Ni color center in diamond
A magneto-optical study of the 1.4 eV Ni color center in boron-free synthetic
diamond, grown at high pressure and high temperature, has been performed in
magnetic fields up to 56 T. The data is interpreted using the effective spin
Hamiltonian of Nazar\'e, Nevers and Davies [Phys. Rev. B 43, 14196 (1991)] for
interstitial Ni with the electronic configuration and effective
spin . Our results unequivocally demonstrate the trigonal symmetry of
the defect which preferentially aligns along the [111] growth direction on the
(111) face, but reveal the shortcomings of the crystal field model for this
particular defect.Comment: 12 pages, 13 figures, submitted to PR
Stratigraphy of a diamond epitaxial three-dimensional overgrowth using doping superlattices
International audienceThe selective doped overgrowth of 3D mesa patterns and trenches has become an essential fabrication step of advanced monolithic diamond-based power devices. A novel methodology is proposed here, combining the overgrowth of plasma-etched cylindrical mesa structures with the sequential growth of doping superlattices. The latter involve thin heavily boron doped epilayers separating thicker undoped epilayers in a periodic fashion. Beside the classical shape analysis under the scanning electron microscope relying on the appearance of facets corresponding to the main crystallographic directions and their evolution toward slow growing facets, the doping superlattices were used as markers in oriented cross-sectional lamellas prepared by Focused Ion Beam and observed by Transmission Electron Microscopy. This stratigraphic approach is shown here to be applicable to overgrown structures where faceting was not detectable. Intermediate growth directions were detected at different times of the growth process and the periodicity of the superlattice allowed to calculate the growth rates and parameters, providing an original insight into the planarization mechanism. Different configurations of the growth front were obtained for different sample orientations, illustrating the anisotropy of the 3D growth. Dislocations were also observed along the lateral growth fronts with two types of Burger vector: bsub01-1 = 1/2 [01-1] and bsub112 = 1/6 [112]. Moreover, the clustering of these extended defects in specific regions of the overgrowth prompted a proposal of two different dislocation generation mechanisms
Subkelvin tunneling spectroscopy showing Bardeen-Cooper-Schrieffer superconductivity in heavily boron-doped silicon epilayers
Scanning tunneling spectroscopies in the subKelvin temperature range were
performed on superconducting Silicon epilayers doped with Boron in the atomic
percent range. The resulting local differential conductance behaved as expected
for a homogeneous superconductor, with an energy gap dispersion below +/- 10%.
The spectral shape, the amplitude and temperature dependence of the
superconductivity gap follow the BCS model, bringing further support to the
hypothesis of a hole pairing mechanism mediated by phonons in the weak coupling
limit.Comment: 4 pages, 3 figure
TEM study of defects versus growth orientations in heavily boron-doped diamond
International audienceHeavy boron-doping layer in diamond can be responsible for the generation of extended defects during the growth processes (Blank et al., Diam. Relat. Mater. 17, 1840 (2008) [1]). As claimed recently (Alegre et al., Appl. Phys. Lett. 105, 173103 (2014) [2]), boron pair interactions rather than strain-related misfit seems to be responsible for such dislocation generation. In the present work, electron microscopy observations are used to study the defects induced by heavy boron doping in different growth plane orientations. Facets of pyramidal Hillocks (PHs) and pits provide access to non-conventional growth orientations where boron atoms incorporation is different during growth. TEM analysis on FIB prepared lamellas confirm that also for those growth orientations, the generation of dislocations occurs within the heavily boron-doped diamond layers. Stacking faults (SFs) have been also observed by high resolution transmission electron microscopy (HREM). From the invisibility criteria, using weak beam (WB) observation, ½ [1-10] and 1/6 [11-2], Burger vectors have been identified. Their generation behavior confirms the mechanism reported by Alegre et al. where local in-plane strain effects induced at the growing surface of the diamond lattice by the neighboring of several boron atoms cause the generation of such extended defects
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