Semi-empirical and ab initio calculations of the optical properties of semiconductor superlattices

摘要

The birefringence of GaAs/oxidized AlAs superlattice has recently provided interesting applications to non-linear optics laser devices. GaAs/vacuum superlattices are a possible model for multilayers formed by GaAs and a wide-gap oxide. They are not only a model system, in fact free standing GaAs films can be produced. First, we have calculated the electronic states and the optical properties of GaAs/AlAs and GaAs/vacuum superlattices within a semi-empirical pseudopotential framework. The features in the optical spectra are well reproduced and the peak positions agree with experiments. Nevertheless, the optical anisotropy cannot be correctly described without the inclusion of local field effects. Thus, we have performed {it ab initio} calculations of the birefringence, within the Time Dependent Density Functional Theory (TDDFT). Neglecting local field effects, we confirm the results of semi-empirical calculations. When local field effects are included agreement with experiments can be obtained.