Band-gap reduction and band alignments of dilute bismide III–V alloys

Adding a few atomic percent of Bi to III--V semiconductors leads to significant changes in their electronic structure and optical properties. Bismuth substitution on the pnictogen site leads to a large increase in spin-orbit splitting ΔSO at the top of the valence band (Γ₈ᵥ-Γ₇ᵥ) and a large reduction in the band gap, creating unique opportunities in semiconductor device applications. Quantifying these changes is key to the design and simulation of 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% and 6.25%), the effects of adding Bi on the valence- and conduction-band edges, and the band offset between these dilute alloys and their III--V 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 lowered, and both effects contribute to the sizable band-gap reduction. Changes in band gap and ΔSO are notably larger in the arsenides than in the antimonides. We also predict cases of band-gap inversion (Γ6c below Γ₈ᵥ) and ΔSO larger than the band gap, which are key parameters for designing topological materials and for minimizing losses due to Auger recombination in infrared lasers.