Book excerpt: This book offers a thorough survey of long wavelength infrared semiconductor emitters based primarily on quantum wells and superlattices. Featuring contributions from the most prominent researchers in the field, this volume allows readers to compare different types of lasers as well as examine investigations of potential far-infrared/terrahertz sources. This is an essential reference for researchers, engineers and graduate students who wish to obtain comprehensive knowledge about infrared semiconductor sources and recent developments in this field.