Two‐dimensional precipitates associated with stacking faults in layer semiconductors have previously been put forward to explain transport properties of these crystals, especially their remarkable electrical anisotropy. High‐field cyclotron resonance behavior, among others, can be accounted for by two‐dimensional accumulation layers in the vicinity of these defects. Direct evidence for the existence of these defects has been obtained by electron microscopy and x‐ray microprobe analysis in indium selenide. Planar faults act like sinks for impurity atoms. This accounts for the unique behavior of layer compounds which exhibit intrinsic behavior (low apparent carrier concentration—high mobilities) even with high (100 ppm) initial doping levels. Optical, transport, and magnetotransport properties at low temperature can be explained along this model. As regards the applications of indium selenide to the photovoltaic conversion of solar energy, the existence of these defects explains most features of this semiconductor in this respect: (i) Its comparatively low effective diffusion length parallel to thecaxis. (ii)p‐ ton‐type switching under thermal annealing which allows fabrication ofp‐njunctions. (iii) Low apparent carrier density which precludes abrupt profiles forp‐nstructures.
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