Free-carrier absorption in metal-oxide semiconducting nanostructures

Abstract

The free-carrier absorption, in semiconductors gives significant information on electron-phonon interaction as well as optical properties of the material. In this work, quantum mechanical theory of free carrier absorption in metal oxide semiconducting nanostructure is presented. Zinc oxide (ZnO) a well-known and versatile metal oxide is ann-type semiconductor under non-stoichiometric conditions. In the present work, the case of non-degenerate electrons being scattered by acoustic phonons via deformation potential coupling is considered. The radiation field, responsible for optical transitions, is assumed to be polarized in the plane of the layer of the free-standingZnO nanostructure. In a free-standing nanostructure the energy of electron is quasi continuous due to spatial quantization. The variation of absorption coefficient with the photon frequency, thickness of the nanostructure, temperature and carrier density is presented. In order to investigate the effect of doping on free-carrier absorption, the results obtained with ZnO are compared with those obtained for aluminum doped ZnO. The calculations indicate that doping results in significant change in free-carrier absorption spectrum due to modification in the phonon spectrum. The study of free-carrier absorption gives a better understanding of optical properties of transparent conducting oxides.