Coulomb-Well Effects in Magnetooptical Spectra of (In, Ga)As/GaAs Multiple Quantum Well Structures

Abstract

Introduction. In pronounced type II QWs excitons are spatially indirect which makes their oscillator strength much smaller than the exciton oscillator strength in type I QWs. However, optical spectra of (In,Ga)As/GaAs QWs show pronounced light-hole exciton transitions, which contradicts the model of spatially indirect excitons [1, 2]. The aCoulomb wello model resolves this problem supposing that the light-hole excitons are spatially direct. Electron±hole attraction is described in this model by introducing a one-dimensional effective potential created by an electron which confines the light hole in the direction normal to the QW plane. An additional hole confinement in QWs due to its Coulomb attraction to the electron has been described theoretically for the case of type I QW with infinite barriers in [3]. The aCoulomb wello was assumed to be parabolic, which yields equidistant hole energy levels. The parabolic approximation provides good agreement with experimental data on the fine excitonic structure in zero-dimensional microcrystals CdS and CdSe where the model of infinite barriers is reasonable. In our case, however, there is no barrier for the light hole at all, so that approach for describing the aCoulomb wello effect needs to be substantially modified. Experimentally, aCoulomb wello effects on the excitonic spectrum can be revealed in the fine structure of excitonic transitions which requires very narrow spectral lines and correspondingly high quality samples.