Impurity-related optical-absorption spectra inGaAs−Ga1−xAlxAssuperlattices with an in-plane magnetic field

Abstract

The effects of applied magnetic fields on the binding energy and the optical-absorption spectra associated with transitions from the first Landau valence level to a shallow donor-impurity band in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\ensuremath{-}\mathrm{G}\mathrm{a}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ superlattices are studied for magnetic fields applied parallel to the interfaces of the heterostructure. The donor-related magneto-absorption spectra are calculated within the effective-mass approximation using a variational procedure. Electron and hole magnetic envelope wave functions were obtained by an expansion in terms of sine functions. We consider a homogeneous donor distribution in the superlattices and analyze the theoretical impurity-related magnetoabsorption spectra for superlattices with different well widths, barrier lengths, and for various applied magnetic fields. We observed that the impurity binding energy decreases as the impurity approaches the barrier for all magnetic fields. For impurities located at the center of the wells the binding energy always increases with the applied magnetic field. The main feature found in the theoretical spectra was an absorption edge associated with transitions involving impurities at the center of the wells. The energy for the peak position shows a linear dependence for magnetic fields higher that 4 T. For lower fields the dependence is nonlinear. Also, we found that the intensity of the peak increases with the applied magnetic field.