Modeling the near-gap refractive index properties of semiconductor multiple quantum wells and superlattices

Near-gap dielectric properties of multiple quantum wells (MQW´s) and superlattices (SL´s) are studied theoretically. A new approach to calculating MQW and SL optical constants is described, and is used to explore the optical properties of lattice-matched and strained-layer structures in III-V material systems of current interest for integrated optoelectronics. In our approach, the complex permittivity tensor is first obtained directly from band structures and wavevector-dependent optical matrix elements for a given MQW or SL, which are calculated using a superlattice K·p model at energies near the band edges and tight-binding supercell calculations for energies deeper in the bands. Polarization-dependent refractive indices and extinction coefficients follow directly. The band structure partitioning scheme used in this work allows for accurate description of the band-edge features in the optical constants, which arise primarily from near-gap band structure, as well as the large background contribution arising from absorption properties far above the band gap energy. Refractive index spectra obtained using this approach are shown to be in close agreement with available experimental data. Finally, we apply this approach to the study of polarization anisotropies in strained MQW´s and to the design of strain-compensated SL´s for polarization-insensitive integrated waveguide applications