Plasmon dispersion and electron heating in a drifting two-dimensional electron gas

We present Raman-scattering and photoluminescence measurements on a laterally drifting two-dimensional electron gas (2DEG) formed at a GaAs-${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As heterojunction. The backscattering geometry employed allows both the direction, parallel, antiparallel, or perpendicular to the drift direction, and magnitude of the in-plane scattering wave vector to be varied. For a fixed wave vector the drift current produces a Doppler shift and broadening of the intrasubband plasmon Raman peak. For small drift velocities the energy shift is linear, and in opposite directions for the Stokes and anti-Stokes spectra, but becomes nonlinear for large drift velocities, and in the same direction in both cases. This change in behavior is ascribed to increasing carrier density with drift. Single-particle relaxation times were determined from the broadening of the plasmon Raman peaks. The ratio of the intensities of the Stokes and anti-Stokes plasmon peaks provides an estimate of the 2DEG temperature under drift conditions; this increased considerably with drift current, as confirmed by the high-energy tail of the band-gap photoluminescence from the 2DEG.