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We report the fully self-consistent calculations of the nonlinear optical properties of superlattices. The materials investigated are monolayer superlattices with GaP grown on the the top of InP, AlP, and GaAs (110) substrates. We use the full-potential linearized augmented plane-wave method within the generalized gradient approximation to obtain the frequency-dependent dielectric tensor and the second-harmonic-generation susceptibility. The effect of lattice relaxations on the linear optical properties is studied. Our calculations show that the major anisotropy in the optical properties is the result of strain in GaP. This anisotropy is maximum for the superlattice with the maximum lattice mismatch between the constituent materials. In order to differentiate the superlattice features from the bulklike transitions, an improvement over the existing effective-medium model is proposed. The superlattice features are found to be more pronounced for the second order than the linear optical response, indicating the need for full supercell calculations in determining the correct second-order response.
Sharma et al. (Wed,) studied this question.