CORRELATION LENGTHS FOR SCATTERING POTENTIALS IN 2-DIMENSIONAL ELECTRON GASES

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 th e quantum lifetime was significantly smaller in the bias-cooled sample than for normal cooling and also that the field dependence of the amp litude was functionally different. This is attributed to a roughening of the scattering potential which results when correlations between th e DX centres are suppressed. To explain the functional change in the f ield dependence it is necessary to consider the confinement effects as sociated with scattering potentials that have correlation lengths smal ler than the Debye wavelength of the electrons. The bias cooling techn ique enables the characteristic length scale of the scattering potenti al to be changed, in the same sample, and at the same carrier density.