First-principles investigation of BAs and B_xGa_1-xAs alloys

Using first-principles calculations in the generalized gradient approximation, the electronic properties of BAs and B_xGa_1 - xAs alloys are studied. At the Brillouin-zone centre, the lowest conduction band is the three-degenerate p-like \varGamma_\rm 15c state rather than s-like \varGamma_\rm 1c state, and the conduction band minimum (CBM) is along the \varDelta line between the \varGamma and X points-at approximately 11/14(1,0,0)2\pi /a. With boron content at 0%--18.75%, B_xGa_1 - xAs alloys have a small (2.6\,eV) and relatively composition-independent band-gap bowing parameter, the band-gap increases monotonically by \sim18 meV/B% with increasing boron content. In addition, the formation enthalpies of mixing for B_xGa_1 - xAs alloys with boron content at 6.25% and 12.5% are calculated, and the large formation enthalpies may explain the difficulty in alloying boron to GaAs.