PIEZOELECTRIC CONTROL OF DOPING AND BAND-STRUCTURE IN THE CROSSED GAP SYSTEM GASB/INAS

We describe the use of strain induced piezoelectric fields to modify the doping and band profiles of GaSb/InAs heterostructures in both the semiconducting and semimetallic regimes. The piezoelectric fields lead to substantial absorption enhancement as well as significant carrier density increases in [111] oriented samples over their [001] equivalents. Strain relaxation is shown to reduce the strength of the piezoelectric field at large layer thicknesses, giving similar carrier densities in both [001] and [111] structures, indicating that the band offsets are probably independent of crystal orientation. Hole cyclotron resonance masses have been observed for the first time in "intrinsic" superlattices and are in the range 0.08-0.20m0. The high hole masses and crossed sets of Landau levels from the electrons and holes result in strong pinning of the Fermi energy in the semimetallic superlattices which we find leads to an interchange of oscillatory behaviour of the Hall and longitudinal resistivity components, as compared to a unipolar system.