We experimentally investigated terahertz photomixing operation at room temperature in an InGaP/InGaAs/ GaAs two-dimensional plasmon-resonant photomixer incorporating grating-bicoupled dual-gate structure. Photoelectrons drifting into a high-density plasmon cavity grating from an adjacent low-density one extensively excite the plasmon resonance, resulting in emission of terahertz radiation. A vertical cavity formed between the two-dimensional plasmon grating plane and an indium-tin-oxide mirror at the back surface gains the radiation. Self-oscillation initially at around 4.5 THz excited by a dc-photo carrier component was reinforced by the photomixed differential-frequency excitation at 4.0 and 5.0 THz. This indicates a possibility of injection-locked oscillation of the photomixer in the terahertz frequency band.

Accumulation of non-equilibrium longitudinal optical (LO) phonons (termed hot phonons) is considered as a possible cause for limitation of frequency of operation of GaN-based high-electron-mobility transistors (HEMTs). The experimental data on noise temperature of hot electrons at a microwave frequency as a function of supplied electric power is used to extract information on hot phonons: the hot-phonon lifetime, the equivalent hot-phonon temperature, the effective occupancy of hot-phonon states involved into electron-LO-phonon interaction. The possible ways for controlling the hot-phonon effect on electron drift velocity through variation of electron density, channel composition, and hot-phonon lifetime are discussed. The expected dependence of hot-electron drift velocity on hot-phonon lifetime is confirmed experimentally. A self-consistent explanation of different frequency behaviour of InP-based and GaN-based HEMTs is obtained from a comparative study of hot-phonon effects.