The past three decades have been a period where useful current and
voltage instabilities in solids have progressed from exciting research
problems to a wide variety of commercially available devices. Materials
and electronics research has led to devices such as the tunnel (Esaki)
diode, transferred electron (Gunn) diode, avalanche diodes, real-space
transfer devices, and the like. These structures have proven to be very
important in the generation, amplification, switching, and processing of
microwave signals up to frequencies exceeding 100 GHz. In this treatise
we focus on a detailed theoretical understanding of devices of the kind
that can be made unstable against circuit oscillations, large amplitude
switching events, and in some cases, internal rearrangement of the
electric field or current density distribution. The book is aimed at the
semiconductor device physicist, engineer, and graduate student. A
knowledge of solid state physics on an elementary or introductory level
is assumed. Furthermore, we have geared the book to device engineers and
physicists desirous of obtaining an understanding substantially deeper
than that associated with a small signal equivalent circuit approach. We
focus on both analytical and numerical treatment of specific device
problems, concerning ourselves with the mechanism that determines the
constitutive relation governing the device, the boundary conditions
(contact effects), and the effect of the local circuit environment.
