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Register a new userEquation of state of single-crystal cubic boron phosphide
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Added by
Oleksandr Kurakevych
Publication date
2014
fields
Physics
and research's language is
English
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The 300 K equation of state of cubic (zinc-blende) boron phosphide BP has been studied by in situ single-crystal X-ray diffraction with synchrotron radiation up to 55 GPa. The measurements have been performed under quasi-hydrostatic conditions using a Ne pressure medium in a diamond anvil cell. A fit of the experimental p-V data to the Vinet equation of state yields the bulk modulus B0 of 179(1) GPa with its pressure derivative of 3.3(1). These values are in a good agreement with previous elastic measurements, as well as with semiempirical estimations.
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Boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) Type Ib diamond substrates using microwave plasma assisted chemical vapor deposition. A modification in surface morphology of the film with increasing boron concentration in the plasma has been observed using atomic force microscopy. Use of nitrogen during boron doping has been found to improve the surface morphology and the growth rate of films but it lowers the electrical conductivity of the film. The Raman spectra indicated a zone center optical phonon mode along with a few additional bands at the lower wavenumber regions. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. However, shrinkage and upshift of Raman line was observed in the film that was grown in presence of nitrogen along with diborane in process gas.
With the best overall electronic and thermal properties, single crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors requires overcoming doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional doping in SCD without inducing graphitization transition or lattice damage can be readily realized with thermal diffusion at relatively low temperatures by using heavily doped Si nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancy exchange boron doping mechanism that occur at the bonded interface between Si and diamond. We further demonstrate selectively doped high voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high voltage power conversion systems and for other novel diamond based electronic devices. The novel doping mechanism may find its critical use in other wide bandgap semiconductors.
We report accurate measurements of the equation of state (EOS) of cubic boron nitride by x-ray diffraction up to 160 GPa at 295 K and 80 GPa in the range 500-900 K. Experiments were performed on single-crystals embedded in a quasi-hydrostatic pressure medium (helium or neon). Comparison between the present EOS data at 295 K and literature allows us to critically review the recent calibrations of the ruby standard. The full P-V-T data set can be represented by a Mie-Gr{u}neisen model, which enables us to extract all relevant thermodynamic parameters: bulk modulus and its first pressure-derivative, thermal expansion coefficient, thermal Gr{u}neisen parameter and its volume dependence. This equation of state is used to determine the isothermal Gr{u}neisen mode parameter of the Raman TO band. A new formulation of the pressure scale based on this Raman mode, using physically-constrained parameters, is deduced.
The ultrahigh thermal conductivity of boron arsenide makes it a promising material for next-generation electronics and optoelectronics. In this work, we report measured optical properties of cubic boron arsenide crystals including the complex dielectric function, refractive index, and absorption coefficient in the ultraviolet, visible, and near-infrared wavelength range. The data were collected at room temperature using spectroscopic ellipsometry as well as transmission and reflection spectroscopy. We further calculate the optical response using density functional and many-body perturbation theory, considering quasiparticle and excitonic corrections. The computed values for the direct and indirect band gaps (4.25 eV and 2.07 eV) agree well with the measured results (4.12 eV and 2.02 eV). Our findings contribute to the effort of using boron arsenide in novel electronic and optoelectronic applications that take advantage of its demonstrated ultrahigh thermal conductivity and predicted high ambipolar carrier mobility.
During past years, a number of reports have been published on synthesis of tetragonal allotrope of boron, t-B52 phase. However, no unambiguous characterization of the crystal structure has been performed to the present time, while remarkable variation of the a/c lattice-parameter ratio raises strong doubts about its uniqueness. Here the Rietveld refinement of the crystal structure of the high pressure - high temperature boron phase synthesized by a direct solid-state transformation of rhombohedral beta-B106 at 20 GPa and 2500 K has been reported for the first time. Although this boron allotrope belongs to the t-B52 type, its structure can be considered as pseudo-cubic with the a/c ratio of sqr(2).
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