Energy and momentum relaxation of hot electrons inGaN/AlGaN

Abstract

We report the experimental studies of hot-electron energy andmomentum relaxation in the steady state in GaN/AlGaN HEMTstructures with a high two-dimensional electron density of n = 1.5×1013 cm-2. From the LO-phonon-scattering-limitedcomponent of the mobility we obtain for the LO phonon the energy ofℏω~90 meV and the momentum relaxation time of τm~4 fs. Drift velocity versus electric field characteristics obtained from the pulsed I-V measurementsshow that, at TL = 77 K, the drift velocity saturates atvd = 1.0×107 cm s-1 at electric fields inexcess of E~7.5 kV cm-1, and at TL = 300 K it saturates at vd~5×106 cm s-1, at anelectric field of around E~10 kV cm-1. Electrontemperature as a function of applied electric field is obtainedby comparing the measured electric field dependence of the mobility µE at a fixed lattice temperature, with thelattice temperature dependence of the mobility at a fixed lowelectric field. The electron energy loss rate is thendetermined from the electron temperature dependence of thepower loss using the power balance equations. The effect of hot-phonon production on the observed momentum and energyrelaxation of hot electrons is discussed within the frameworkof a theoretical model, which was originally developed forIII-V material systems and has been adapted for a two-dimensionalelectron gas in GaN, and in which phonon drift is neglected.