Photon drag investigations of current relaxation processes in a two-dimensional electron gas

We have investigated the photon drag current that is excited by an infrared laser beam in the plane of the two-dimensional electron gas of GaAs/Al0.35 Ga0.65As multiple-quantum-well systems. An analysis of the: spectral respon se, measured with the picosecond infrared pulses of the wavelength-tunable free electron laser source FELIX, is presented for different doping schemes and examined as a function of temperature and intensity. The influence of the subband-selective scattering by a delta doping is explored, which demon strates that the photon drag spectral response allows the determination of the momentum relaxation time ratio, R = tau (1)/tau (2), of the electrons i n the ground and excited subbands. The relaxation time ratio is found to be surprisingly constant over a large temperature range. The variation of the ratio with intensity can be attributed to heating of the electron gas, who se temperature exceeds 1000 K at saturation intensity.