Theory of the Photovoltaic Effect in Semiconductors

The detailed theory of “surface photovoltage” is developed for the case of small signals in Si and Ge. In addition to the usual factors considered (such as the spreading of space charge during illumination etc.) other important effects such as the trapping of photocarriers on the surface and the photoconductivity in the space charge region are taken into consideration. Δ n involves the surface trapping parameters in addition to the electron—hole pair generation rate. A convenient set of approximate equations are chosen, from the usual relations, to describe the dependence of the photo e.m.f. on temperature, surface potential, and the parameters of the local centres. It is shown that under appropriate simplifying assumptions the expressions obtained reduce to those formerly described.