The possibility of using of nonequilibrium effects in the electronic gas as basis of functioning of quantum devices are researched in this book. Quantum phenomena and nonequilibrium phenomena are equally important for mesoscopic structures. The sources of nonequilibrium states of the electronic gas are localized in the small neighborhood of heterogeneities of potential relief generated by heteroboundaries and concentration gradients. The quantum devices with electric characteristics similar to conventional elements of microelectronics and functioning in THz frequency region can be created by using of nonequilibrium quantum effects. Designs of such devices are considered and their characteristics are calculated in the book.