Recently, there has been a considerable upsurge of interest in heavily doped semiconductors. This interest is due primarily to the expanding range of applications of such. materials. Moreover, the heavy doping of semiconductors produces new effects (the forma tion of impurity aggregates, the appearance of allowed states in the forbidden band, etc J, which are of great interest in solid-state physics. The rapid growth in the number of papers on heavily doped semiconductors makes it difficult to review the results obtained so far. Therefore, many investigations carried out in 1966-7, par ticularly those on AIIIBV semiconductors, are not discussed in the present monograph, which represents the state of the knowledge in 1965. Nevertheless, the author hopes that, in spite of this, the book will be useful. An attempt is made, first, to review investigations of heavily doped semiconductors from a certain viewpoint and, sec ondly, to suggest some ideas (Chap. 5) which may be controversial but which are intended to stimulate further studies of heavily doped semiconductors which can be regarded as a special case of dis ordered systems. The work of American scientists investigating heavily doped semiconductors, in particular the efforts of E. O. Kane, J. 1. Pan kove, R. N. Hall, R. A. Logan, W. G. Spitzer, F. A. Trumbore, and many others, is well known to Soviet investigators. It gives me pleasure to learn that Western readers will now have an - v vi PREFACE portunity to become acquainted with the work done in the USSR.

First-generation semiconductors could not be properly termed "doped- they were simply very impure. Uncontrolled impurities hindered the discovery of physical laws, baffling researchers and evoking pessimism and derision in advocates of the burgeoning "pure" physical disciplines. The eventual banish ment of the "dirt" heralded a new era in semiconductor physics, an era that had "purity" as its motto. It was this era that yielded the successes of the 1950s and brought about a new technology of "semiconductor electronics". Experiments with pure crystals provided a powerful stimulus to the develop ment of semiconductor theory. New methods and theories were developed and tested: the effective-mass method for complex bands, the theory of impurity states, and the theory of kinetic phenomena. These developments constitute what is now known as semiconductor phys ics. In the last fifteen years, however, there has been a noticeable shift towards impure semiconductors - a shift which came about because it is precisely the impurities that are essential to a number of major semiconductor devices. Technology needs impure semiconductors, which unlike the first-generation items, are termed "doped" rather than "impure" to indicate that the impurity levels can now be controlled to a certain extent.