Solid-state electronic devices are used as sources of radiation for frequencies below, typically 150 GHz as well as for frequencies over 10Terahertz (l=30 mm). The gap between ~150GHz - 10THz is covered by such sources as optically pumped far infrared (FIR) gas lasers and free electron lasers. Within this "Terahertz Gap", no convenient solid-state source of FIR radiation is available, although there is a great demand for such a source in a variety of applications. The overall aim of this proposal is to investigate two approaches to developing FIR emitter devices based on composite multiple quantum wells (QWs) and superlattices (SLs) containing electron and hole gases. The first approach is based on investigations of radiative processes involving single electron transitions; electron and hole gases in the devices use both unstrained and strained quantum confinements. The second approach will utilize collective electron excitations, plasmons and magnetoplasmons. The results expected from this Project will provide new information on both fundamental and technological aspects of FIR emission, and in the final stage of the work demonstrator devices will be developed.