Book excerpt: Publisher's Note: Products purchased from Third Party sellers are not guaranteed by the publisher for quality, authenticity, or access to any online entitlements included with the product. This comprehensive text is aimed at graduate level students and researchers, breaking down the complexities of fabrication, use, and maintenance of heterojunctions. Topics include: introduction to quantum mechanics, Potential barriers and wells, electronic energy levels in periodic potentials, tunneling through potential barriers, distribution functions and density of states, optical properties of interband and intersubband transitions, electrical properties, techniques and measurements, growth issues, devices: Detectors and emitters.