THEORY OF POTENTIAL MODULATION IN LATERAL SURFACE SUPERLATTICES - II - PIEZOELECTRIC EFFECT

We have calculated the piezoelectric coupling between a two-dimensiona l electron gas and the stress field due to a lateral surface superlatt ice, a periodic striped gate. Stress is assumed to arise from differen tial contraction between the metal gate and semiconductor. The piezoel ectric potential is several times larger than the deformation potentia l and generally gives the dominant coupling. It depends on the orienta tion of the device and vanishes on a (100) surface if the current flow s parallel to a crystallographic axis. Most devices, however, are fabr icated parallel to {011} cleavage planes in which case the piezoelectr ic potential is at a maximum. There are several sources of screening, including the partly occupied donors in a typical GaAs-AlxGa1-xAs hete rostructure. We also consider different elastic models for the gate. T he best agreement with experiment is obtained if the force is distribu ted over the interface between the gate and semiconductor, rather than being concentrated at its ends.