Hot-electron energy relaxation time in Ga-doped ZnO films

Hot-electron energy relaxation time is deduced for Ga-doped ZnO epitaxial layers from pulsed hot-electron noise measurements at room temperature. The relaxation time increases from similar to 0.17 ps to similar to 1.8 ps when the electron density increases from 1.4 x 10(17) cm(-3) to 1.3 x 10(20) cm(-3). A local minimum is resolved near an electron density of 1.4 x 10(19) cm(-3). The longest energy relaxation time (1.8 ps), observed at the highest electron density, is in good agreement with the published values obtained by optical time-resolved luminescence and absorption experiments. Monte Carlo simulations provide a qualitative interpretation of our observations if hot-phonon accumulation is taken into account. The local minimum of the electron energy relaxation time is explained by the ultrafast plasmon-assisted decay of hot phonons in the vicinity of the plasmon-LO-phonon resonance. (C) 2015 AIP Publishing LLC.