The conductance of a GaAs-based suspended quantum point contact (QPC) equipped with lateral side gates has been experimentally studied in the absence of the external magnetic field. The half-integer conductance plateau (0.5×2e2/h) has been observed when an asymmetric voltage between the side gates is applied. The appearance of this plateau has been attributed to the spin degeneracy lifting caused by the spin-orbit coupling associated with the lateral electric field in the asymmetrically biased QPC. We have experimentally demonstrated that, despite the relatively small g-factor in GaAs, the observation of the spin polarization in the GaAs-based QPC became possible after the suspension due to the enhancement of the electron-electron interaction and the effect of the electric field guiding. These features are caused by a partial confinement of the electric field lines within a suspended semiconductor layer with a high dielectric constant.

We study electron transport in suspended semiconductor microstructures fabricated from AlAs/GaAs membranes containing a high mobility two-dimensional electron gas. In quantizing magnetic fields, a reflection of edge current channels from the border of suspended area is observed resulting in the absence of vanishing magnetoresistance in the quantum Hall effect (QHE) regime. Relocation of this border out of the Hall bar revives the QHE. We have also found that the critical current of the breakdown of QHE in suspended samples is three times lower than in non-suspended samples due to the peculiarity of heat transport in the membranes.

The experimental study of the suspended GaAs quantum point contact (QPC) equipped with in-plane side gates reveals that, under such conditions, the QPC constriction has an unusual triple-channel structure involving three conductive channels with the quantized conductance selectively driven by the gates. The analysis of capacitance coefficients and channel widths allows us to conclude that the channels are narrow, compared to the lithographic constriction of the QPC, and that two of the channels are located along the constriction edges, while the other one passes along the middle line. The suspended QPC with the selectively driven triple-channel structure represents a device with an enhanced functionality. The electrostatic mechanism of the channel formation, specific for trench-type suspended QPCs with side gates, is discussed.