Electronic Properties of Doped Semiconductors

First-generation semiconductors could not be properly termed "e;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 "e;pure"e; physical disciplines. The eventual banish- ment of the "e;dirt"e; heralded a new era in semiconductor physics, an era that had "e;purity"e; as its motto. It was this era that yielded the successes of the 1950s and brought about a new technology of "e;semiconductor electronics"e;. 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 "e;doped"e; rather than "e;impure"e; to indicate that the impurity levels can now be controlled to a certain extent.