Correlation lengths for scattering potentials in two-dimensional electron gases

摘要

Shubnikov - de Haas measurements have been made in a `bias-cooled' GaAs/GaAlAs heterojunction, i.e. a gated sample cooled with a negative bias voltage to suppress the formation of DX centres. It was found that the quantum lifetime was significantly smaller in the bias-cooled sample than for normal cooling and also that the field dependence of the amplitude was functionally different. This is attributed to a roughening of the scattering potential which results when correlations between the DX centres are suppressed. To explain the functional change in the field dependence it is necessary to consider the confinement effects associated with scattering potentials that have correlation lengths smaller than the Debye wavelength of the electrons. The bias cooling technique enables the characteristic length scale of the scattering potential to be changed, in the same sample, and at the same carrier density.