Structural and thermodynamic properties of cubic boron nitride (c-BN) under pressure and for varying temperature are studied by molecular-dynamics (MD) simulation with the use of a well-tested Tersoff potential. Various physical quantities including the thermal expansion coefficient and heat capacity are predicted. Our simulation is extended to study liquid boron nitride at various densities.

A detailed characterization of the impurity centers involved in the photoluminescence (PL) of p-type CdTe doped with arsenic (As) and antimony (Sb) has been performed. The PL spectrum has been measured from 1.35 eV up to the band edge and as a function of temperature (4.2 up to 30 K). In addition to the familiar broad PL line centered at 1.45 eV and present in undoped and doped materials, the doped samples exhibit a new band near 1.54 eV showing a fine structure composed of two peaks whose intensities vary with temperature. The observed longitudinal optical (LO) phonon replicas associated with the zero-phonon lines, at 1.45 eV and 1.54 eV, respectively, are characterized by a Huang-Rhys factor S=1.3±0.1 and S=0.30±0.02. The various electron-hole recombination processes are explained by means of a simple analytic model correlating the position of the zero-phonon lines to the relative intensities of the phonon side bands. The model accounts for the chemical shift of the defect centers and describes the effect of the charge carrier LO-phonon interaction in the framework of the adiabatic approximation within the envelope function approach. Comparison between theory and experiment leads to the following values for the effective Bohr radii: aAs=(10.6±0.1) Å, aSb=(10.3±0.1) Å, and ionization energies: EAs=(58±2) meV, ESb=(61±2) meV. It also leads to conclude to the presence of native shallow donors with binding energy ED=(13±2) meV and of deeper native acceptor complexes with effective Bohr radius aA=(6.1±0.1) Å and ionization energy EA=(157±2) meV.

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We have performed an ab initio investigation for a series of boron compounds, BP, BAs, and BSb, and have compared their structural and electronic properties with those of c-BN. The calculations are performed using a plane-wave expansion within the local density approximation and the pseudopotential approximation. Results are given for lattice constants, bulk moduli, band structures, and band-gap pressure coefficients. The electronic properties of these compounds are shown to have features that differ from those of other III-V materials. We found that the direct-band-gap pressure coefficient in boron compounds is nearly independent of the anion substitutions. As a result, this trend is similar to the one resulting from cation substitutions in other zinc-blende compounds. This is another anomalous behaviour which can be characterized by reversing the standard assignments for the anion and cation in these compounds.

We present first-principles calculations of the bonding properties for the series of boron compounds BP, BAs, and BSb. The plane-wave pseudopotential approach to density functional theory in the local density approximation has been used to calculate the equilibrium properties, i.e., the ground-state energy, the lattice constant, the bulk modulus, its pressure derivative, and the ionicity factor. The valence electron density is used to study the modification of the bonding with respect to different pressures. The calculated electronic charge densities present an anomalous behaviour which can be characterized by reversing the standard assignments for the anion and cation in these compounds. The competition between the ionic and the covalent character in these materials is discussed in relation to the charge transfer. Estimates of the ionicity and its pressure derivative for the series of boron compounds are presented. The distribution of the valence charge density suggests that the bonding in these materials is less ionic than in other zinc-blende compounds.