Etching of in an oxidizing etchant under intense local illumination was found to be selective and, moreover, to be a powerful method for the characterization of this material. A flat bottom hole is etched into the illuminated surface region of n‐type , whereas a mesa structure forms on p‐type material. Thus, it is possible to determine the conductivity type of very small surface areas. Height and depth of those structures both decrease with increasing doping level. Striations, precipitates, and decorated dislocation lines are revealed with excellent resolution even in undoped or semi‐insulating samples. By measuring photovoltages between an illuminated and a dark electrode in , the surface photovoltaic effect was shown to be the origin of selective photoetching.
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F. Kuhn-Kuhnenfeld (1972) studied this question.