Electronic structure and band alignment of dilute III-V_1-xBi_x alloys

Adding a few atomic percent of Bi to conventional III-V semiconductors leads to significant changes in their electronic structure and optical properties. Bismuth substituting on the pnictide site in III-Vs leads to an increase in spin-orbit splitting ?_SO at the top of the valence band (Γ8 − Γ7) and a substantial reduction in band-gap. Quantifying these changes is key to designing and simulating electronic and optoelectronic devices. Using hybrid functional calculations, we predict the band-gap of III-Vs (III=Al, Ga, In and V=As, Sb) with low concentrations of Bi (3.125%, 6.25%) and the band alignment to their parent compounds. As expected, adding Bi raises the valence-band maximum (VBM); however, contrary to previous assumptions, the conduction-band minimum (CBM) is also significantly affected; both effects contribute, almost equally, to the sizeable band-gap reduction. These changes are predicted to be larger in the arsenides than in the antimonides, and explained in terms of atomic size and electronic mismatches. Our results provide accurate parameters and guiding principles for designing devices based on dilute III-V bismide alloys.