Optically Pumped Terahertz Radiation Sources Based on Impurity Carrier Transitions in Quantum Wells

A review of the results of studies of terahertz radiation associated with impurity electron transitions in n-doped GaAs/AlGaAs quantum wells under conditions of interband optical excitation of nonequilibrium charge carriers is presented. The principles of radiation generation and methods of controlling its intensity are described: a decrease in the lifetime of electrons at impurity levels due to stimulated interband radiation and the introduction of a compensating acceptor impurity.