Hot-electron transport in GaAs/Ga1−xAlxAs quantum-well structures

We present a review of the experimental results of the steady-state hot-electron energy and momentum relaxation for longitudinal transport in GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Al}}_{\mathit{x}}$As quantum wells. The results of the current work and the work reported in the literature indicate that the nonequilibrium population of LO phonons, contrary to the assumptions made in conventional theories, is randomized in K space. Therefore, the production of hot phonons not only reduces the energy relaxation rate but also enhances the momentum relaxation rate. The latter reduces the drift velocity at high fields and hence inhibits negative differential conductivity via real-space transfer or intervalley transfer. The results are compared with a comprehensive theoretical model involving nondrifting hot phonons and scattering from remote impurities and interface roughness. It is shown that hot-phonon effects increase with increasing three-dimensional carrier concentration and the agreement between the theory and the experiments carried out by three independent research groups is excellent.