We have reached the double conclusion: that invention is choice, that
this choice is imperatively governed by the sense of scientific beauty.
Hadamard (1945), Princeton University Press, by permission. The great
majority of all sources and amplifiers of microwave energy, and all
devices for receiving or detecting microwaves, use a semiconductor
active element. The development of microwave semiconductor devices, de-
scribed in this book, has proceeded from the simpler, two-terminal,
devices such as GUNN or IMPATT devices, which originated in the 1960s,
to the sophisticated monolithic circuit MESFET three-terminal active
elements, of the 1980s and 1990s. The microwave field has experienced a
renais- sance in electrical engineering departments in the last few
years, and much of this growth has been associated with microwave
semiconductor devices. The University of Massachusetts has recently
developed a well recognized program in microwave engineering. Much of
the momentum for this pro- gram has been provided by interaction with
industrial companies, and the influx of a large number of
industry-supported students. This program had a need for a course in
microwave semiconductor devices, which covered the physical aspects, as
well as the aspects of interest to the engineer who incorporates such
devices in his designs. It was also felt that it would be im- portant to
introduce the most recently developed devices (HFETs, HBTs, and other
advanced devices) as early as possible.