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

Abstract

Ultrafast electronic and phononic processes are investigated in voltage-biased GaN-basedtwo-dimensional channels of interest for heterostructure field-effect transistors. Theaccumulation of non-equilibrium longitudinal optical phonons (hot phonons) is treated forAlGaN/GaN, AlGaN/AlN/GaN, AlGaN/GaN/AlN/GaN, and AlInN/AlN/GaN structuresin terms of the hot-phonon temperature and hot-phonon lifetime. The hot-phononeffect on hot-electron energy relaxation and hot-phonon number relaxation isextracted from an experimental investigation of hot-electron fluctuations and powerdissipation. The measured equivalent hot-phonon temperature is nearly equalto the hot-electron temperature. The hot-phonon lifetime varies in the rangefrom 150 to 800 fs and depends on electron density, temperature, and suppliedelectric power. The experimental dependence of the hot-phonon lifetime on thehot-phonon mode occupancy is unique—neither Raman optical-photon scattering noroptical-phonon-assisted intersubband absorption has, as yet, provided any experimentaldata of this sort.