Two-dimensional holes in GaAs Higfets: Fabrication methods and transport measurements

We present a fabrication process and results of transport measurements of a number of p-channel heterojunction-insulated-gate field-effect transistors (HIGFETs). Without intentional doping in HIGFETs, the disorder is likely to be less than that in the modulation-doped samples. We established a process that eliminates the well-known gate leakage problem. The hole density in our devices can be continuously tuned down to a record low value of 7 × 10 ⁸cm^-2. Remarkably, such a dilute system (with Fermi wavelength approaching 1 μm) exhibits a non-activated conductivity that grows with temperature approximately as a power law at sufficiently low temperatures. We contrast it with the activated transport found in more disordered samples and discuss possible transport mechanisms in this strongly-interacting regime.