A tunable terahertz-band oscillator based on a two-well nanostructure with a coherent electron subsystem

A theory of coherent resonance tunneling of electrons in a two-well nanostructure (TWNS) in the presence of a strong electromagnetic field is developed. The TWNS consists of two identical tunnel-coupled quantum wells to which a dc electric field is applied. Radiative transitions occur between two levels that arise due to the interwell interference and the dc electric field. The wavefunctions and polarization currents in the TWNS are found in the case of a strong electromagnetic field, and the oscillation power is determined as a function of the coherent pumping current and the parameters of the structure. It is shown that oscillations are possible in the relevant terahertz band, with fine frequency tuning by a dc field. It is found that the interference of electrons between quantum wells plays a crucial role. This interference significantly suppresses the effect of the electromagnetic field on the resonance tunneling and enhances the oscillation up to the highest possible level. It is proved that there exists an optimal regime of strong-field oscillations without inverse population and saturation, which are inherent in conventional lasers. (c) 2005 Pleiades Publishing, Inc.