The electrical response of two-dimensional electron gas to vibrations of a nanomechanical cantilever containing it is studied. Vibrations of perpendicularly oriented cantilevers are experimentally shown to change oppositely the conductivity near their bases. This indicates the piezoelectric nature of electromechanical coupling. A physical model is developed, which quantitatively explains the experiment. It shows that the main origin of the conductivity change is a rapid change in the mechanical stress on the boundary between suspended and non-suspended areas, rather than the stress itself.PACS numbers: 85.85.+j, 73.50.Dn, 77.65.Ly Most of the currently studied low-dimensional electron systems are fabricated from a two-dimensional electron gas (2DEG) embedded in a semiconductor bulk. A classical example of such a system is a 2DEG in GaAs/AlGaAs heterostructures. However, selective etching of a sacrificial layer (often called surface nanomachining) gives an opportunity to create also a 2DEG embedded in a thin membrane freely suspended over a substrate [1]. The nanostructures fabricated from such membranes are mechanically moveable with their movement affecting electron transport and conductivity [2]. Such electromechanical coupling gives an opportunity to probe mechanical motion at the nano-scale and it could be used to study various interesting mechanical phenomena, such as "phonon lasing" [3] and the quantum-limited motion of an artificially made object [4]. Moreover, it opens up new prospects for studying non-trivial transport phenomena in 2DEG under unusual conditions, namely, in the presence of additional mechanical degrees of freedom, and for creating nanoelectromechanical systems (NEMS). For example, papers [5,6] show that the electron transport through a quantum point contact placed on a micromechanical resonator is sensitive to mechanical vibrations. Papers [2,7,8] demonstrate that diffusive conductive channels in 2DEG can also be used as nanoelectromechanical transducers.The two fundamental key points arising in the context of NEMS are the physical mechanisms underlying actuation and transduction of the nanomechanical motion. The question about the actuation in NEMS with 2DEG is addressed elsewhere [7], while, in the present paper, we focus on the transduction mechanism. Most of the papers considering GaAs/AlGaAs-based suspended systems contain a proposal that a 2DEG embedded in a resonator is sensitive to its vibrations due to the change in the density of a 2DEG that screens the piezoelectrically induced bound charge [2,5,6,9]. However, there is a lack of experimental evidence for this hypothesis.In the present paper, we experimentally demonstrate that the dominant physical mechanism making a 2DEG sensitive to NEMS mechanical vibrations is associated with the piezoelectric effect and show the sensitivity magnitude. We propose also a physical model giving an independent estimate for the value of electron density change consistent with the experiment. According to the model, the local change in the 2DE...
Driven vibrations of a nanoelectromechanical system based on GaAs/AlGaAs heterostructure containing two-dimensional electron gas are experimentally investigated. The system represents a conductive cantilever with the free end surrounded by a side gate. We show that out-of-plane flexural vibrations of the cantilever are driven when alternating signal biased by a dc voltage is applied to the in-plane side gate. We demonstrate that these vibrations can be on-chip linearly transduced into a low-frequency electrical signal using the heterodyne down-mixing method. The obtained data indicate that the dominant physical mechanism of the vibrations actuation is capacitive interaction between the cantilever and the gate.
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.
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