INFRARED-SPECTROSCOPY AND TRANSPORT OF ELECTRONS IN SEMICONDUCTOR SUPERLATTICES

Infrared spectroscopy is a powerful tool for revealing some key properties of electrons in the minibands of semiconductor superlattices. Some theoretical foundations of superlattice physics as well as the experimental work on infrared absorption will be reviewed in this article. After a discussion of the energy levels (minibands, donor states) and the effect of external electric and magnetic fields on the miniband structure, a framework for the description of optical transitions between and within minibands is developed. Experiments on inter- and intraminiband as well as on cyclotron resonance absorption are presented in some detail. The most striking phenomena observed in this context are the van Hove singularities in the miniband joint density of states, the thermal quenching of miniband conductivity, and magnetic miniband breakdown. Finally, transport and infrared emission experiments are summarized.