Magneto-Optical Properties of Heterojunctions, Quantum Wells and Superlattices

Abstract

In a magnetic field the continuous dispersion relations of the bandstructure are split into discrete Landau levels. The energy separation between these Landau levels can be measured optically, and this way information about the bandstructure is obtained. Since transitions are never infinitely sharp in real systems, additional information can be obtained from broadening. In the first part of this paper intraband absorption (cyclotron resonance) in heterojunctions and quantum wells in a magnetic field perpendicular to the layer, with emphasis on the consequences of non-parabolicity will be described. Furthermore several aspects which can contribute to the observed cyclotron linewidth will be mentioned. In the second part a discussion of interband (valence to conduction band) absorption will be given. In particular the effect of the complex valence bandstructure on the experimental results will be described. As in interband absorption both electrons and holes are involved, the effect of their interaction (exciton formation) on the results will be discussed. In the last part interband absorption in a superlattice with a magnetic field parallel to the layers will be discussed. Here a different effect of the magnetic field will be employed, namely that carriers in a magnetic field describe circular orbits in a plane perpendicular to the field, which have an orbit size that can be comparable to the superlattice periodicity. Therefore this type of experiments probes transport through the layers of the superlattice.