Interband optical absorption in semiconductors.

A unified, treatment of the direct. Intel-band optical absorption in semiconductors in the presen\u27.-;.- f external static electric and magnetic fields., is presented in tne framework of the \u27effective mass approximation1. A general expression for tne absorption coefficient Is derived, wnlcn in une appr..?par at el.y which may provide the values of effective masses .in alilerent bands. The experimental conditions,, and the validity criterion for the perturbation theory., are thoroughly discussed. Some attention :.i s paid to the study of magnetic field induced surface states. Whereas suen states have been observed recently in metals, there is no experimental or theoretical evidence as to whether or not these states exist in semiconductors. We have theoretically predicted that such states do in fact exist even in semiconductors. The experimental conditions under which surface states may be detected experimentally in semiconductors are discussed. The arguments are supported with quantitative calculations,, where possible. Throughout the entire presentation we nave restricted ourselves to the study of direct band gap semiconductors. - 11