Theory of carrier mobility in polar-semiconductors

Abstract

A theory of the mobility of charge carriers (electrons or holes) in polar semiconductors, where a band description is valid, has been developed. The system chosen is Lead Chalcogenide (PbX, where X is S, Se, or Te). Both the filled and conduction bands in such systems have over-lapping s and p characters. The essential approach of the theoretical formulation is to start with such perturbed one electron states which include the effect of interband transitions caused by lattice vibrations. In view of the polar nature of the systems such a band mixing is pronounced for the optical mode. In the scattering mechanism both the role of acoustic and optical modes is taken into account, whereas for the interband transitions the optical or polar modes in the reststrahlen region are assumed to be important. It is found that the two phonon processes are important for the transport problem. The temperature dependence of the mobility in the high temperature region is of the form μ = μ0T^-5/2, in very good agreement with the observed behaviour. There is close order of magnitude agreement between theory and experiments for the value of μ⁰.