Electric Field Distribution in Polarized Photoconductors

Persistent internal polarization is shown to result from the accumulation of trapped charge near the surface layers of a photoconductor. At equilibrium it is predominantly of a bulk nature, rather than being localized in individual grains. The charge layers are found to be restricted to narrow regions from 5 to 10 microns from each surface. This distance is almost independent of sample thickness and polarizing voltage. While the external field is still applied, the equilibrium state of polarization is such that between the layers the field approaches zero. This is concluded from the fact that the buildup and release of polarization proceed at the same rate when equal exciting intensities are used.