Theory of Superlinear Photoconductivity in CdS and Related Materials

Several theoretical considerations are developed in order to make the treatment of phenomena related to superlinear photoconductivity in CdS and related materials more consistent with experimental data on these materials. Special attention has been given to the way in which various shallow trap distributions affect the dependence of photoconductivity on light intensity in the superlinear range. The nature of the breakpoints or transitionpoints between superlinear and nonsuperlinear regions is clarified. An explanation is offered for the common occurrence of hysteresis in photoconductivity vs light intensity curves in materials exhibiting superlinear photoconductivity. Finally the possibility of observing Auger recombination because of the very small electron capture cross section of sensitizing centers in these materials is discussed. Illustrative experimental results in CdS and GaAs crystals are included.