Frequency limits of terahertz radiation generated by optical-phonon transit-time resonance in quantum wells and heterolayers

We develop an analytical model based on a few generalized parameters of bulk materials and two-dimensional (2D) structures which enables us to analyze the main features of terahertz (THz) radiation generation caused by optical-phonon transit-time resonance. In the framework of such a model and direct Monte Carlo simulations it is shown that for the same material (i) generation conditions are the same in quantum wells and heterolayers characterized by the same parameter of electron localization in the 2D channel and (ii) a considerable increase up to 5 times of the high-frequency cutoff for THz radiation generation is predicted in going from 3D to 2D transport.