Effect of Photoexcitation on the Mobility in Photoconducting Insulators

Abstract

The Hall mobility of carriers in photoconducting insulators can be varied over an appreciable range by the effects of photoexcitation. Such a variation can result either (1) from a change in the density of scattering centers as the result of a change in the occupation of imperfection centers, or (2) from the initiation of two-carrier conductivity. Suitable use of the phenomena involved in the photo-Hall effect can lead not only to knowledge about carrier density, carrier sign, and carrier mobility, but also about the charge on imperfection centers, and to an independent determination of the cross section of imperfection centers. Experiments on CdS and CdSe single crystals with conductivities lying between ${10}^{-9\mathrm{}}$ and ${10}^{-1\mathrm{}}$ mho/cm are described to illustrate the potentialities of the technique. The results emphasize both the importance that changes in mobility can play in normal photoconductive processes, and the importance of hole conductivity under suitable circumstances.