M. V. Budantsev

Electron transport in suspended semiconductor structures with two-dimensional electron gas

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.

Actuation and transduction of resonant vibrations in GaAs/AlGaAs-based nanoelectromechanical systems containing two-dimensional electron gas

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 features of ballistic electron transport in a suspended quantum point contact

A suspended quantum point contact and the effects of the suspension are investigated by performing identical electrical measurements on the same experimental sample before and after the suspension. In both cases, the sample demonstrates conductance quantization. However, the suspended quantum point contact shows certain features not observed before the suspension, namely, plateaus at the conductance values being non-integer multiples of the conductance quantum, including the “0.7-anomaly.” These features can be attributed to the strengthening of electron-electron interaction because of the electric field confinement within the suspended membrane. Thus, the suspended quantum point contact represents a one-dimensional system with strong electron-electron interaction.

High-amplitude dynamics of nanoelectromechanical systems fabricated on the basis of GaAs/AlGaAs heterostructures

Nonlinear vibrations of nanoelectromechanical beam fabricated from the GaAs/AlGaAs heterostructure containing two-dimensional electron gas are investigated. The measurement of time-averaged conductance is shown to be a sensitive method for the nanomechanical motion detection. The possibilities to excite high-amplitude (up to 20u2009nm) mechanical vibrations and to effectively detect them using the simple conductance measurement make such systems promising for practical applications. High-amplitude vibrations of the beam are shown to demonstrate softening nonlinearity. This can be attributed to the bending of the beam due to Euler buckling instability caused by the compressive stress though GaAs/AlGaAs heterostructures are typically considered as stress-free.

Hysteretic phenomena in a 2DEG in the quantum Hall effect regime, studied in a transport experiment

The nonequilibrium state of a two-dimensional electron gas (2DEG) in the quantum Hall effect (QHE) regime, manifested in the hysteresis of magnetoresistance of a 2DEG with a constriction, has been experimentally studied. The large amplitude of the hysteresis enabled us to make the consistent phenomenological description of the hysteresis. We performed minor loop measurements, recovered the anhysteretic curve, and studied the time dependence. We showed that the hysteresis has significant phenomenological similarities with that of magnetization of ferromagnets, showing multistability, jumps of relaxation, and having the anhysteretic curve. The difference is manifested itself in an unusual inverted (anti-coercive) behavior of the hysteresis. The time relaxation of the hysteresis has fast and slow regimes, similar to that of non-equilibrium magnetization of a 2DEG in QHE regime pointing to their common origin. We studied the dependence of the hysteresis loop area on the lithographic width of the constriction and found the threshold value of width ∼1.35 μm. This points to the edge nature of the nonequilibrium currents (NECs) and allows us to determine the width of the NECs area (∼0.5 μm). We suggest the qualitative picture of the observed hysteresis, based on non-equilibrium redistribution of the electrons among the Landau level states and assuming huge imbalance between the population of bulk and edge electronic states.

Ballistic magnetotransport in a suspended two-dimensional electron gas with periodic antidot lattices

The magnetoresistance of suspended semiconductor nanostructures with a two-dimensional electron gas structured by periodic square antidot lattices is studied. It is shown that the ballistic regime of electron transport is retained after detaching the sample from the substrate. Direct comparative analysis of commensurability oscillations of magnetoresistance and their temperature dependences in samples before and after suspension is performed. It is found that the temperature dependences are almost identical for non-suspended and suspended samples, whereas significant differences are observed in the nonlinear regime, caused by direct current passage. Commensurability oscillations in the suspended samples are more stable with respect to exposure to direct current, which can be presumably explained by electron–electron interaction enhancement after detaching nanostructures from the high-permittivity substrate.

Ballistic thermopower of suspended semiconductor Hall bars with two dimensional electron gas

We study ballistic electron transport in suspended semiconductor nanostructures containing high mobility two dimensional electron gas structured with periodical square lattice of artificial scatters — antidots. Thermopower demonstrates magnetic field commensurability oscillations resulting from geometrical resonances similar to those earlier observed in magnetoresistance, thus indicating the retaining of the ballistic regime in thermopower measurement on suspended structures and the validity of the Mott rule in this case. In spite of peculiarities of the heat transport in suspended structures leading to the observed anomalies in non-linear effects, the amplitude of thermopower oscillations remains unchanged after the suspension. This can be explained by short Thouless time compared to the time of electron- phonon interaction.

Ballistic electron transport in structured suspended semiconductor membranes

We study ballistic electron transport in freely suspended AlAs/GaAs microstructures containing a high mobility two-dimensional electron gas with square lattice of antidots. We found that the magnetoresistance of the samples demonstrates commensurability oscillations both for the case of non-suspended and suspended devices. The temperature dependence of the commensurability oscillations is similar for both cases. However, the critical dc current, that suppresses these oscillations, in suspended samples is three times lower than in non-suspended ones. The observed phenomenon can be explained by peculiarities of the heat transport in membranes.

Inverted hysteresis of magnetoresistance of a 2DEG at integer filling factors

We report on an observation of giant hysteresis of longitudinal magnetoresistance of a constriction placed in a macroscopic two‐dimensional electron gas at integer filling factors. The most striking feature of observed phenomenon is the inverted form of hysteresis loops which is manifested in advanced system response to a small change of external magnetic field. We found that the resistance in the region of hysteresis loop relaxes in a stepwise manner, that is phenomenologically similar to Barkhausen jumps.

Electron Transport: From Nanostructures to Nanoelectromechanical Systems

Electron transport in nanostructured systems, with characteristic sizes that are less than the mean free path of the electron or the phase relaxation length of its wave functions, becomes so nontrivial that it requires reinterpretation and rephrasing of the term resistance itself. The examples of such systems are solid state realizations of electron Sinai billiards. An intriguing development in semiconductor “nanostructuring” technology has been nanostructure fabrication from suspended conducting semiconductor membranes detached from the bulk. Such structures, featuring a mutual coupling of electrical and mechanical degrees of freedom, are referred to as nanoelectromechanical systems. We describe the results of investigations into electron transport phenomena in semiconductor nanostructures, which also involve suspended nanostructures detached from the bulk.