ADVANTAGES OF A PIEZOELECTRIC FIELD IN A QUANTUM-WELL

We have compared the properties of strained quantum wells grown along the [001] and [111] directions. In the latter case a piezoelectric field is created which we have found to have several advantages. We have analyzed in some detail quantum wells n-doped on one side, by performing self-consistent subband structure calculations in the local-density approximation and calculating scattering times due to remote ionised impurity scattering, which is an important limiting factor for the mobility. We find that the scattering times can be increased considerably by increasing the separation between the electrons and the ionised donors. We also predict electron densities in excess of 3 x 10(12) cm-2, which should be useful for improving High Electron Mobility Transistors (HEMTs).