Abstract
The conditions for THz radiation generation caused by electron transite-time resonance in momentum and real spaces under low-temperature optical-phonon emission are analysed. Main attention is paid to transverse electromagnetic waves generation in: (i) 3D bulk materials and (ii) 2D quantum heterosctructures as well as (iii) longitudinal current instabilities in submicron and overmicron n+nn+ diodes. It is found that in all the cases considered the nitride-based materials and structures are the most preferable for the THz radiation generation as compared with III-V compounds. Furthermore, 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.