Pressure dependence of optical transitions in ordered GaP/InP superlattices

Abstract

We have calculated the pressure coefficients α of a few optical transitions in (001), (111), (110), and (201) GaP/InP ordered superlattices using ab initio methods. The equilibrium atomic geometries under hydrostatic pressure are obtained by direct minimization of the elastic enthalpy. We find that (i) the pressure coefficient of the lowest energy transition is uniformly high, due to the Γ1c character of the conduction-band minimum; (ii) the pressure coefficient of the transition to the second lowest conduction state at Γ̄ distinguishes the (111)-oriented (CuPt) superlattice (α=4.0 meV/kbar) from the remaining structures (α≂−2 meV/kbar). This is so because in CuPt we have L folding, while in the other structures we have X folding; (iii) the calculated pressures for the Γ→X crossover are 45, 43, 12, and 16 kbar for the (001), (111), (110), and (201) superlattices, respectively. These trends reflect the zero-pressure Γ1c–X1c energy separation and the Γ1c pressure coefficient of these structures.