Electron relaxation times in high-carrier-density GaAs-(Ga,Al)As heterojunctions

From the amplitudes of the Shubnikov--de Haas (SdH) oscillations in magnetotransport measurements on different GaAs-(Ga,Al)As heterojunctions with two occupied subbands, the subband single-particle relaxation times have been extracted. The lowest-subband single-particle relaxation time appears to be modulated by the second-subband SdH oscillation periodicity, indicating the importance of screened long-range Coulomb scattering and nonlinear intersubband scattering. Parallel-field and near-parallel-field magnetoresistance measurements reveal that the presence of the second-subband electrons affects the lower-subband electrons in two different ways: the onset of intersubband scattering leads to a decrease of the transport scattering time in the lower subband, while the additional screening provided by the upper-subband electrons leads to an increase of the single-particle relaxation time.