Photoluminescence studies of current-induced nonequilibrium states in magnetically quantized two-dimensional electron gases

We report studies by optical techniques of current-induced nonequilibrium electron populations in magnetically quantized two-dimensional electron gases. Increasingly marked current-dependent changes with magnetic field are observed in both the energy and the intensity of the main photoluminescence features. The magnetic-field dependence of the relaxation time of nonequilibrium population following a current pulse is qualitatively in line with the severe momentum constraints on one-phonon emission. However, a theoretical treatment of this mechanism shows stronger field dependence, proportional to B-4, than that found experimentally proportional to B-2, indicating the importance of parallel relaxation channels. We suggest these may involve the diffusion of excited electrons via intra-Landau-level transitions to centers in the Hall bar where relaxation can occur via inter edge-state transitions.