Chapter 5 Optical Absorption above the Fundamental Edge

Abstract

Publisher Summary The measurement of the intrinsic absorption of semiconductors is a powerful tool for studying the energy-band structure of solids. The measurement of the fundamental absorption edge yields the minimum energy separation between the valence and conduction bands and the nature of the transitions involved. As one increases the photon energy from the fundamental edge, the first structure to be expected in the fundamental absorption spectrum of the III-V compounds corresponds to transitions from the ┌ 7 valence band, split from the top valence bands by spin-orbit interaction, to the lowest conduction band at k = 0. At even higher energies, the absorption spectrum of the III-V compounds shows considerable structure. This structure is also very similar to the structure observed in the absorption spectrum of other materials of the diamond and zinc-blende families. This chapter describes the absorption spectrum of very thin germanium films, identify the observed structure, and carry over this identification to the III-V compounds by means of several theoretical and semi-empirical rules.