M. B. Semenov

Controllable dissipative tunneling in an external electric field

We have studied the problem of controllable dissipative tunneling in the system of tunnel-binding quantum dots (quantum molecules) and in the “AFM/STM cantilever tip-quantum dot” system, which was simulated by a double-well oscillator potential interacting with a heat-bath in an external electric field. We show that theoretical results qualitatively describe some experimental I–V curves for “the AFM/STM cantilever tip-zirconium quantum dot” system. These experimental curves were obtained in the Research Institute of Physics and Technologies at the State University of Nizhniy Novgorod.

Observed two-dimensional tunnel bifurcations in an external electric field

The controllability problem for two-dimensional dissipative tunneling in the system of tunnel-coupled quantum dots (a quantum molecule), interacting quantum molecules, and the system “ACM/CTM cantilever tip-quantum dot” simulated by a 2D oscillator potential in a heat bath and an external electric field is investigated. The obtained results qualitatively correspond to the separate experimental volt-ampere characteristics (VACs) for the system “platinized ACM/CTM cantilever tip-gold quantum dot” obtained at Scientific-Research Physical-Technical Institute with Nizhnii Novgorod State University. The previously-predicted 2D tunnel bifurcations with dissipation for the case of interacting particles tunneling in parallel are found to be experimentally observed and stable.

The features of tunneling current-voltage characteristics in a combined atomic force/scanning tunneling microscope system with quantum dots of colloidal gold

Tunneling current—voltage characteristics for growing quantum dots of colloidal gold in a combined atomic force/scanning tunneling microscope system were obtained. It was assumed that ionic conduction produces the largest contribution to the tunneling current. The tunneling current—voltage characteristics were compared qualitatively to the theoretical curve of the field dependence of the probability of 2D dissipative tunneling that was calculated taking the influence of two local phonon modes of a wide-bandgap matrix into account. It was demonstrated that the experimental and theoretical curves agree qualitatively. This suggests that the dissipative tunneling mechanism may produce a contribution to the tunneling current through a growing quantum dot under a cantilever needle. This current may be amplified in clusters with sizes of 1–5 nm in thinner films.

The influence of local phonon modes in a wide-band matrix on the tunnel current-voltage characteristics of quasi-zero-dimensional structures

Experimental results on the visualization of the density of states in InAs/GaSa(001) quantum dots that were obtained by tunnel atomic-force microscopy in an ultrahigh vacuum are presented. A one-dimensional (1D) model of dissipative quantum tunneling is proposed for describing experimental current-voltage characteristics of a tunnel contact between an atomic force microscope probe and the surface of InAs/GaAs (001) quantum dots. It was found that the influence of two local modes of the wide-band matrix on the probability of 1D dissipative tunneling leads to the appearance of several randomly spaced peaks in the field dependence. It was shown that the theoretical dependence agrees qualitatively with experimental the current-voltage characteristic of the atomic force microscope tip and the surface of InAs/GaAs(001) quantum dots.

The Influence of the McCumber Parameter on Parametric Amplification of High-Frequency Radiation by Josephson Junctions

The influence of the internal capacity of a Josephson junction on the parametric amplification of external electromagnetic radiation was studied in terms of a resistively and capacitively shunted junction model. The influence of the McCumber parameter on parametric amplification was clarified. It is shown that the additional regions of amplification can occur near subharmonic Shapiro steps in the case of Josephson junctions with internal capacity.

Controllable influence of the photodielectric effect to process of the submillimeter waves spread in quantum dots structures in an external magnetic field

The registration possibility of the excited states for impurity complexes A+ + e (acceptor with an additional hole, which interacts with an electron, localized in the quantum dot ground state) because of their contribution to the dielectric permeability of the semiconductor quasi-zero structure under intraband optical transitions of electrons in an external magnetic field, has been theoretically analyzed. It is shown, that effective control of the photodielectric effect (PDE) by modifying of the electronic adiabatic potential and the electron wave function is possible in an external magnetic field. It is found, that new possibilities for the PDE-control are appeared in an external magnetic field. These effects are important for applications in semiconductive nanoelectronics: for example, for controllable influence on the spread of submillimeter waves in nanostructures; for detectors of infrared — radiation with controllable parameters; for method of the impurities spectroscopic studies in semiconductive nanostructures.

Kinetic coefficients of semiconductor superlattices in high-frequency electromagnetic fields

The problem of electric stability for a semiconductor superlattice is a crucial one for the practical realization of sub-THzand THz-based devices. For example, it is well-known that the development of instabilities and the formation of electric domains in a superlattice placed in a dc electric field leads to the destruction of the THz gain [1]. Therefore, the main problem in the realization of superlattice-based THz devices is finding operational conditions which simultaneously allow one to achieve gain at THz frequencies and to avoid destructive spacecharge instabilities. Correct description of instability effects requires taking into account spatial-dispersion effects. Such approach for the case of dc biased superlattice was formulated by Ignatov and Shashkin [1–3] and Bonilla et al. [4–6]. As a rule, a drift-diffusion model is used to describe transport and high-frequency properties of superlattices in the quasistatic case. In particular, this model allows taking into account spatial-dispersion effects. However, as it will be shown below, this model can give incorrect results because the correct dependence of kinetic coefficients on the amplitudes of dc and ac fields as well as temperature in the quasistatic case can be obtained only from the Boltzmann and Poisson equations. Note that the analysis of kinetic coefficients of superlattice can give the important information about spatial-dispersion effects and instabilities by analogy with the Gunn effect. In this paper, we present an approach from which general expressions for the field-dependent average drift velocity, Maxwell frequency and diffusion coefficient are derived starting from the exact solution of Boltzmann equation. As a rule the diffusion coefficient is obtained from the Einstein relation in the framework of driftdiffusion model. However the Einstein relation is not always applicable for strong fields [5, 7]. In connection with it, the calculation of the diffusion coefficient is an important separate question. In this paper we obtain the diffusion coefficient from the exact solution of Boltzmann equation and show that it is sufficiently different from the diffusion coefficient obtained from the Einstein relation. Let us consider a superlattice under the action of the dc field E0 directed along the x-axis and the strong ac field E1 cos(ω1t). Our main goal is to find and analyze the kinetic coefficients of semiconductor superlattice in quasi-static approximation starting from the exact solution of the kinetic equation and taking into account spatial-dispersion effects connected with a small perturbation E2 cos(ω2t− k2x). In the following, we will use the standard dispersion relation in the tight-binding approximation:

The effects of two-dimensional bifurcations and quantum beats in a system of combined atomic force and scanning tunneling microscopes with quantum dots

The field and temperature dependence of the probability of two-dimensional dissipative tunneling is studied in the framework of one-instanton approximation for a model double-well oscillator potential in an external electric field at finite temperature with account for the influence of two local phonon modes for quantum dots in a system of a combined atomic force and a scanning tunneling microscope. It is demonstrated that in the mode of synchronous parallel transfer of tunneling particles from the cantilever tip to the quantum dot the two local phonon modes result in the occurrence of two stable peaks in the curve of the 2D dissipative tunneling probability as a function of the field. Qualitative comparison of the theoretical curve in the limit of weak dissociation and the experimental current–voltage characteristic for quantum dots that grow from colloidal gold under a cantilever tip at the initial stage of quantum-dot formation when the quantum dot size does not exceed 10 nm is performed. It is established that one of the two stable peaks that correspond to interaction of tunneling particles with two local phonon modes in the temperature dependence of the 2D dissipative tunneling probability can be split in two, which corresponds to the tunneling channel interference mechanism. It is found that the theoretically predicted and experimentally observed mode of quantum beats occurs near the bifurcation point.

Tunnel volt-ampere characteristics for colloidal gold quantum dots under dissipative tunneling conditions

In this project the tunnel volt-ampere characteristics of colloidal gold quantum dots in a system of combined tunnel and atomic force microscopes were experimentally measured. It is assumed that ionic conductivity contributes for tunnel current the most. A qualitative comparison was made for tunnel volt-ampere characteristics and the theoretical probability curve of 2D-dissipative tunneling under influence of two local wide-band phonon modes. A qualitative agreement was found for theoretical and experimental curves, which indicates the possible contribution of the dissipative tunneling in the current through a quantum dot at the tip of a cantilever, which can be amplified in clusters ranging in size from 1 to 5 nm in thinner films.

Possible mechanisms of conductivity in the combined AFM / STM and growing quantum dots of colloidal gold

We have obtained tunneling current - voltage characteristics for growing quantum dots of colloidal gold in the combined atomic - force and scanning tunneling microscope. It is assumed that the main contribution to current gives the ionic conductivity. A qualitative comparison of the tunneling current - voltage characteristics with the theoretical curve for field dependence of the probability of 2D - dissipative tunneling with the influence of two local phonon modes in wide - band matrix has been fulfilled. A qualitative agreement of the experimental and theoretical curves, suggesting a possible contribution of the dissipative tunneling in the tunnel current through a growing quantum dot under the needle of the cantilever, which can be amplified in clusters ranging in size from 1 to 5 nm in thinner films, has been also established.