GaN-based two-dimensional channels: hot-electron fluctuations and dissipation

Ultrafast electronic and phononic processes are investigated in voltage-biased GaN-based two-dimensional channels of interest for heterostructure field-effect transistors. The accumulation of non-equilibrium longitudinal optical phonons ( hot phonons) is treated for AlGaN/GaN, AlGaN/AlN/GaN, AlGaN/GaN/AlN/GaN, and AlInN/AlN/GaN structures in terms of the hot-phonon temperature and hot-phonon lifetime. The hot-phonon effect on hot-electron energy relaxation and hot-phonon number relaxation is extracted from an experimental investigation of hot-electron fluctuations and power dissipation. The measured equivalent hot-phonon temperature is nearly equal to the hot-electron temperature. The hot-phonon lifetime varies in the range from 150 to 800 fs and depends on electron density, temperature, and supplied electric power. The experimental dependence of the hot-phonon lifetime on the hot-phonon mode occupancy is unique-neither Raman optical-photon scattering nor optical-phonon-assisted intersubband absorption has, as yet, provided any experimental data of this sort.