PROFILE OF PERIODIC POTENTIAL MODULATION PROBED BY MAGNETORESISTANCE OSCILLATION OF A 2-DIMENSIONAL ELECTRON-GAS

We have studied the profile of potential modulation introduced to a Ga As/AlGaAs heterostructure two-dimensional electron gas (2DEG) by a str iped gold gate with period a = 500 nm on the surface. The magnetoresis tance oscillation of 2DEG under one-dimensional periodic potential mod ulation arising from commensurability between the period and cyclotron diameter has been measured as a function of bias voltage applied to t he gold gate. The bias alters both the amplitude and lineshape of the potential seen by 2DEG, with concomitant change in the magnetoresistan ce oscillation. The analysis of the magnetoresistance shows that with a positive bias, the modulation amplitude is considerably reduced and the third harmonic component becomes conspicuous. This suggests that t he ''built-in'' potential modulation, caused mainly by strain resultin g from differential contraction between the gold gate and GaAs, has mo re rectangular landscape, than the potential added by the bias. The st rain-induced third harmonic component accounts for the previously unex plained extra dips in the magnetoresistance traces for a magnetically modulated 2DEG with a ferromagnetic metal gate.