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Schematic cross section of a vacuum FET (not to scale). A H-Si(111) piece is contact bonded to a SOI piece in a vacuum. The H-Si(111) piece has heavily boron-doped (p+) regions to make contact to the 2DHS. In the SOI piece, the shield and the gate are p+ layers formed by double boron ion implantation. Dry etching is used to create the cavity. The arrows depict the electric field. The 2DHS is induced at the H-Si(111) surface in the encapsulated vacuum cavity.
Left axis: mobility as a function of gate voltage at 70 mK and 4.2 K. At 70 mK, the wild fluctuations of the mobility are due to the high contact resistances to the 2DHS. Right axis: Hole density vs gate voltage. The hole densities (triangles) are determined by the magnetic field B at the filling factor minima: . The dashed line is a linear fit. Inset: on the Si(111) piece, Van der Pauw geometry consists of a cloverleaf-shaped 2DHS with a center square, and four heavily boron-doped contacts.
Longitudinal resistances , and Hall resistance vs perpendicular magnetic field B at () and T = 70 mK. Quantum Hall effect is observed near B = 5.2 T. The inset shows an enlarged section of , which exhibits a beating pattern, and the arrow marks the node location (B = 1.14 T).
(a) (), () vs filling factor at V and T = 70 mK. The corresponding magnetic field B is shown on the top axis. The node location (B = 1.14 T) is marked by an arrow. Across the node, the minima change from the odd numbers of to the even numbers of . (b) Fourier power spectra of the SdH oscillations () at different gate voltages. Maximum peak amplitudes are normalized to 1. At V, the solid line is the power spectrum of , and the dotted line is the power spectrum of . (c) Zero-field spin splitting and effective Rashba coefficient as functions of hole density . We do not use a window function in the Fourier transform for the data presented here. If a Hann window is applied, the peak locations shift slightly, and () can change by about 5%. This is shown as an error in Fig. 4(c).
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