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.