Fabrication of samples for scanning probe experiments on quantum spin Hall effect in HgTe quantum wells

We present a fabrication process for devices on HgTe quantum wells through which the quantum spin Hall regime can be reached without the use of a top-gate electrode. We demonstrate that a nominally undoped HgTe quantum well can be tuned from p-type to n-type, crossing through the quantum spin Hall regime, using only a back-gate hundreds of microns away. Such structures will enable scanning probe investigations of the quantum spin Hall effect that would not be possible in the presence of a gate electrode on the surface of the wafer. All processes are kept below 80 degrees C to avoid degradation of the heat-sensitive HgTe quantum wells. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4767362]