Subband quantum scattering times for AlGaAs/GaAs obtained using digital filtering

In this study we investigate both the transport and quantum scattering times as a function of the carrier concentration for a modulation doped Al _0.3Ga_0.7As/GaAs structure. Carriers in the well are generated as a result of the persistent photoconductivity effect. When more than one subband becomes populated, digital filtering is used to separate the components for each of the excited subbands. We find that the quantum scattering time for the ground subband increases initially as the carrier concentration is increased. However, once the second subband becomes populated, the ground subband scattering time begins to decrease. The quantum scattering time for the excited subband is also observed to decrease as the concentration is increased. Our results are consistent with the theoretical results by A. Isihara and L. Smrcka [J. Phys. C 19, 6777 (1986)]. Finally, from the ratio of the transport and quantum scattering times, it is seen that the transport in the well becomes more isotropic as the concentration is increased.