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We have investigated commensurability oscillations in the magnetoresistances of two-dimensional lateral surface superlattices with square patterns and periods of 100 nm. In some of our samples the symmetry of the potential was broken by the presence of stress and strong piezoelectric effects. Oscillations were weak in symmetric samples, but became much stronger for transport along the [01(1) over bar] direction [on a (100) wafer] when the symmetry was broken. For transport along the [010] and [001] directions in the asymmetric samples, the dominant Fourier component in the potential was at an angle of 45 degrees to the transport direction, and the commensurability oscillations had an effective period of 100/root 2 nm. All of these observations are fully in accord with a recent semi-classical theory based on the guiding center drift concept

We have fabricated lateral surface superlattices by etching a strained layer of In0.2Ga0.8As near the surface of a heterostructure. This provides strong modulation of the electron gas while retaining a high electron mobility. The potential arises mainly from strain and the piezoelectric effect, which depends on orientation, and from the change in the surface profile. The fundamental components of these two contributions cancel in one orientation to leave a dominant second harmonic. This effectively halves the period of the superlattice from its lithographic value and provides a promising technique for creating potentials with a period comparable to the Fermi wavelength.

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