Trends in band-gap pressure coefficients in boron compounds BP, BAs, and BSb

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.