Chapter 9 Effects of Free Carriers on the Optical Properties

Abstract

This chapter discusses the effects of free carriers on the optical properties. In semiconductors, the effect of free carriers on the optical properties becomes important at wavelengths longer than the intrinsic absorption edge. Free carriers produce absorption and affect the dispersion at sufficiently long wavelengths. In a radiation field, the current of the carriers has a component in phase and a component out of phase with the electric field. The in-phase current contributes to the conductivity and the out-of-phase component contributes to the susceptibility. In terms of the electronic energy bands of the crystal, the effects of the carriers may be intraband or interband in nature. The intraband effects involve only the energy band that contains the carriers, and will be simply referred to as free-carrier effects. The interband effects involve another energy band.