ABSTRACT
This chapter outlines the theory of optical processes in bulk semiconductors. First of all, the relationship between the absorption coefcient and the refractive index is developed from Maxwell’s equations. This is followed by a classication of different absorption processes in semiconductors. The theory of absorption is then developed by using a semiclassical formalism, rst for the fundamental band-to-band transition in a direct-bandgap semiconductor and next for the intervalence band absorption (IVBA). A simple classical Drude model is employed to treat the free-carrier absorption (FCA). The opposite process of absorption, that is, recombination and luminescence due to direct interband transition, is then introduced. The theory of Auger recombination is developed for the most important transition, while other recombination processes, trap-assisted recombination and surface recombination, are discussed briey. A brief description of carrier-induced changes in the bandgap, and the refractive index, then follows. Finally, the theory of excitonic absorption in direct-gap materials is developed.
