CHARACTERIZATION OF THE TRANSPORT-PROPERTIES OF CHANNEL DELTA-DOPED STRUCTURES BY LIGHT-MODULATED SHUBNIKOV-DE HAAS MEASUREMENTS

The transport properties of channel delta-doped quantum-well structures were characterized by conventional Hall effect and light-modulated Shubnikov-de Haas (SdH) effect measurements. The large number of carriers that become available due to the delta doping of the channel, leads to an apparent degeneracy in the well. As a result of this degeneracy, the carrier mobility remains constant as a function of temperature from 300 down to 1.4 K. The large amount of impurity scattering, associated with the overlap of the charge carriers and the dopants, resulted in low carrier mobilities and restricted the observation of the oscillatory magnetoresistance used to characterize the two-dimensional electron gas by conventional SdH measurements. By light modulating the carriers, we were able to observe the SdH oscillation at low magnetic fields, below 1.4 T, and derive a value for the quantum scattering time. Our results for the ratio of the transport and quantum scattering times are lower than those previously measured for similar structures using much higher magnetic fields. (C) 1995 American Institute of Physics.