Potential modulation by strain in lateral surface superlattices

We have measured the magnitude of the potential modulation below gated one-dimensional lateral surface superlattices fabricated with periods between 60 and 600 nm on a range of GaAs/AlGaAs heterostructures. The magnitude of the modulation was obtained by studying the amplitude of the commensurability oscillations in magnetoresistance, and confirmed by analysis of the low field positive magnetoresistance step. Without gate bias applied, the modulation is generated by strain in Che gates, coupled piezoelectrically to the two-dimensional electron gas. Both magnitude and harmonic content of the potential are in reasonable agreement with a recent theoretical calculation of this coupling, over the full range of periods and for all the structures studied. Away from zero gate bias electrostatic modulation adds to the piezoelectric component. This differs according to the sign of the applied bias. In depletion it increases roughly linearly with-bias and is in good agreement with theoretical estimates, whereas in positive bias it tends to saturate as strong screening in the donor layers develops.