Energy levels of hydrogenic impurities and Wannier excitons in quantum well structures

Abstract

Interest in the study of the behavior of shallow impurity centers and Wannier excitons in superlattices and quantum well structures is fairly recent. This paper reviews briefly both the theoretical and experimental work done in this field in the last two years. Several recent calculations of the energy levels of hydrogenic impurity states and Wannier excitons in quantum well structures, such as Ga1−xAlxAs–GaAs–Ga1−xAlxAs, assuming infinite and finite potential barriers at the interfaces, are reviewed. The behavior of these levels as a function of the quantum well size is discussed. It is shown that the behavior of the energy states of these shallow systems in finite height potential wells is both qualitatively and quantitatively different from that in infinite height potential wells especially in thin (<100 Å) wells. Recent experimental data concerning the variations of the binding energies of shallow acceptors and Wannier excitons as a function of the GaAs quantum well size is reviewed. A comparison between these experimental measurements and the results of recent calculations is presented.