THE PHOTOIONIZATION IN ANISOTROPIC POLAR SEMICONDUCTORS

The photoionization has been considered as an optical transition from the impurity ground state to a continuum state belonging to a conducti on band in semiconductors. The dependence of the photoionization cross -section on photon energy is calculated for a shallow donor impurity t aking into account the effect of the electron mass anisotropy. The int eraction between the electron and the longitudinal optical (LO) phonon is taken into account using Frohlich's coupling and applying the Lee- Low-Pines transformation. The cross-sections involving zero or one pho non are evaluated for a shallow donor in CdS and it is shown that the cross-section is very sensitive to the electron mass anisotropy, the e lectron-phonon coupling, and their combined effect.