Research on intersubband transitions in quantum wells has led to several
practical devices, such as the QWIP (quantum well infrared photodetector)
and the QCL (quantum cascade laser). These are two of the success stories
in using quantum wells for practical device applications. Research activities
in this area have been very intense over the past ten years, resulting in many
new devices that are presently being developed for the market. We therefore
feel that the time is right to collect a comprehensive review of the various
topics related to intersubband transitions in quantum wells. We hope that
this volume will provide a good reference for researchers in this and related
fields and for those individuals- graduate students, scientists, and engineers-
who are interested in learning about this subject.