Theory of the anomalously low band-gap pressure coefficients in strained-layer semiconductor alloys

The band-gap pressure coefficients of III-V ternary semiconductor alloys within strained layers are significantly lower than the bulk binary values and the drop in pressure coefficient, of about 6xmeV/kbar for InₓGa_1-xAs grown on GaAs remains unexplained. Linear elasticity has been used to predict first-order (linear) effects of pressure, but for strained layers, this procedure fails to predict the pressure coefficients. We show that the nonlinear elasticity theory is necessary, and when evaluated with a consistent level of approximation throughout, it accounts for the pressure coefficients, largely through an approximately linear increase of Poisson's ratio with pressure. Earlier experimental data and some photoabsorption results for InₓGa_1-xAs on InP are reviewed and they agree well with values predicted using our analysis.