Linear and second-order optical response of III-V monolayer superlattices

We report the first fully self-consistent calculations of the nonlinear\noptical properties of superlattices. The materials investigated are mono-layer\nsuperlattices with GaP grown on the the top of InP, AlP and GaAs (110)\nsubstrates. We use the full-potential linearized augmented plane wave method\nwithin the generalized gradient approximation to obtain the frequency dependent\ndielectric tensor and the second-harmonic-generation susceptibility. The effect\nof lattice relaxations on the linear optical properties are studied. Our\ncalculations show that the major anisotropy in the optical properties is the\nresult of strain in GaP. This anisotropy is maximum for the superlattice with\nmaximum lattice mismatch between the constituent materials. In order to\ndifferentiate the superlattice features from the bulk-like transitions an\nimprovement over the existing effective medium model is proposed. The\nsuperlattice features are found to be more pronounced for the second-order than\nthe linear optical response indicating the need for full supercell calculations\nin determining the correct second-order response.\n