Amorphous semiconductors

In recent years the physics of amorphous semiconductors has developed into a field so extensive and ramified that it is difficult to review in one paper. Various researchers emphasize different achievements; my choice of these is based on an attempt to give the reader an idea of the breadth of the research—from fundamental questions on electron states and atomic motions to the principles underlying some of the applications. The main difficulty with such a presentation of a more or less consistent picture is that there will necessarily be an inadequate discussion of alternative interpretations, so that the reader may get the mistaken impression that the suggested models were uniquely deduced from the experimental data. Unfortunately, crucial experiments that distinguish between different interpretations are still scarce. Nevertheless, experimental and theoretical work in the last five years have shown that some previously suggested plausible assumptions were incorrect, and the field has achieved, besides its extensive growth, significant progress in the understanding of the fundamental physics.