A non-invasive SOI gating method for probing 2D transport on pristine chemically-terminated Si surfaces

Silicon has a variety of surface terminations available to it in which surface states are passivated and where 2D electron inversion layers are possible through electrostatic gating. In the Kane lab, Si(111) surfaces are terminated with hydrogen using a simple wet-chemical treatment of high-purity, deoxygenated, aqueous NH₄F. Extremely high mobilities, in excess of 300,000 cm²/Vs [1], have been demonstrated in our previous generation devices, and further refinement of these techniques to preserve the pristine nature of these passivated Si surfaces is expected to yield even higher mobilities. To this end, we have developed a new technique to probe these pristine H-Si surfaces using a non-invasive SOI flip-chip gating assembly in which all critical device fabrication is performed on the SOI end. Additionally, our novel device architecture is fully process-compatible with existing UHV halogen-termination (Cl, Br, I) techniques providing a viable solution for 2D transport studies on these surfaces. Architecture details and 77K characterization of 4-terminal devices with newly-incorporated Au depletion gates will be discussed, as well as ongoing low temperature (4K and below) challenges.

[1] T. Kott et al, Phys. Rev. B 89, 041107(R), 2014