Negative spin-orbit bowing in semiconductor alloys

Early measurements on many bulk III-V alloys showed that the spin-orbit splitting Δ₀ at the valence-band maximum (VBM) was universally reduced relative to the average value of the end-point constituents. This led to the assumption, guiding much of the subsequent data analysis, that such alloys universally mix some conduction-band s character into the VBM (``interband coupling''), suppressing Δ₀. Our self-consistent electronic-structure calculations for Ga(As,Sb) show very little s mixing in the VBM and an enhancement of Δ₀. Intraband p-p coupling is shown to dominate the changes in Δ₀.