Transient Response of Grain Boundaries and Its Application for a Novel Light Sensor

Abstract

Grain boundaries in n‐type germanium and silicon carry a negative surface charge and constitute a potential barrier for electrons. The height of this barrier can be increased by applying an electrical pulse across the boundary or decreased by injecting holes. The relaxation time with which the perturbed barrier returns to its equilibrium value is for sufficiently low temperatures very large compared to the time necessary to change the barrier height. A theory of the transient response of a grain boundary to a pulse is given for the low temperature region. It is shown that the application of a pulse of given height results in a barrier height φ_s which is practically independent of the barrier height φ_a prior to the pulse. The transient current, however, depends markedly on φ_a. A novel photosensor based on this phenomenon is described, and preliminary experimental results are reported.