Heat pulse studies of the energy relaxation rate of hot electrons in n-type GaN epilayers

We have measured the energy relaxation rate of hot electrons in GaN over th e temperature range 1-130 K using a non-equilibrium pulse technique. The sa mples were fabricated from an n(+) GaN epilayer grown by MBE on a c-axis sa pphire substrate. In addition we were able to observe directly the emitted phonons. Above 10 K the relaxation rate showed a linear dependence characte ristic of the equipartition regime. Below 10 K, the dependence was P propor tional to T-e(4), consistent with piezoelectric coupling in the so-called ' dirty' limit. In contrast to GaAs, coupling to acoustic phonons was the dom inant energy relaxation mechanism up to the maximum temperature of the expe riment. (C) 1999 Elsevier Science B.V. All rights reserved.