V.N. Murzin

Resonant tunneling and intersubband population inversion effects in asymmetric wide quantum-well structures

Abstract Theoretical estimates and the results of vertical transport and optical investigations in GaAs/AlGaAs structures show that resonant tunneling can lead efficiently to selective depopulation of the levels, resulting in a population inversion and possible stimulated emission due to intersubband transitions between the lowest states in wide-quantum-well structures.

Pulsed-laser deposited protective ‘diamond-like’ carbon coatings on high-Tc superconductors

Abstract The fabrication of diamond-like coating on high- T c superconductors is investigated. Carbon thin films were deposited on YBa 2 Cu 3 O 7 single-crystal film by pulse-laser sputtering of graphite targets. Deposition at room temperature yields diamond-like films with high optical transmission, high resistivity, and good adhesion to unpretreated YBa 2 Cu 3 O 7 . Degradation of superconducting properties or deterioration of mechanical characteristics of YBa 2 Cu 3 O 7 films was not observed after carbon deposition and subsequent low temperature thermocycling. The water-protective properties of these diamond-like coatings were investigated.

Intersubband population inversion under resonance tunnelling in wide quantum well structures

The possibility of intersubband population inversion and the necessary conditions for its achievement in wide quantum well structures with the energy space between the lowest states being lower than the optical phonon energy are considered. Two possible designs are proposed, both using resonant tunnelling for selective depopulation of the lowest subband. The analysis of resonance tunnelling times and intersubband relaxation rates due to various scattering processes is carried out, demonstrating the possibility, at sufficiently low carrier concentrations, of inverted carrier distributions over the lowest subbands under optical pumping or electrical injecting conditions.

Continuous narrow-band amplification tuning effect at terahertz frequencies in double-quantum-well resonant tunneling nanostructures

Abstract. High-frequency response properties of single and double-quantum-well resonant tunneling diodes (RTD) are examined in a wide frequency range, up to terahertz (THz) frequencies, on the base of proposed quantum theory. Numerical solutions of time-dependent Schrödinger equations with open-system boundary conditions in an external electromagnetic field are performed. The numerical solutions take into account the influence of bias DC voltage on electronic states in RTD with finite height and width of barriers both for monoenergetic and for Fermi-distributed electrons in emitter and collector parts of structures. We show that the presence of an additional level in double-quantum-well structures breaks the response symmetry and leads to selective narrow-band frequency amplification, as well as to the effect of amplification frequency tuning at THz frequencies by variation of applied bias voltage. These phenomena predict an increase of gain coefficient and open new perspectives for engineering of novel types of THz oscillators and other high-frequency units.

Magnetic field control of resonant tunnelling and electric field domain stability in wide quantum well GaAs/AlGaAs superlattices

A transverse (in-plane) magnetic field (B = 0–7 T) was used to modify the shape of the tunnelling resonance between electronic states in neighbouring quantum wells of a superlattice and to investigate the effect of the modification of the tunnelling resonance profile on electric field domain stability and self-sustained current oscillations effect in GaAs/AlGaAs superlattices.

Multilevel logic element based on the long-period GaAs/AlGaAs superlattice

Abstract The dynamics of the switching between multistable current branches in weakly coupled GaAs/AlGaAs superlattices was investigated. A multilevel logic device with several stable current states was proposed and the possibility of switching between any selected states by voltage pulses of appropriate amplitude and polarity was demonstrated.

Terahertz narrow-band tune amplification effect in triple-barrier quantum well resonant tunneling nanostructures

Resonant tunneling diode high-frequency study on the base of proposed quantum models and numerical solution of timedependent Schrödinger equation with open-system boundary conditions in external electromagnetic field are performed for single-quantum well and double-quantum well resonant tunneling structures. As shown the presence of privileged additional level in double-quantum well structures breaks response symmetry, leads to narrow-band frequency selective amplification at frequencies equal to energy spacing between levels in neighbouring quantum wells and to selection of portion of emitter electrons that actively interact with external THz electromagnetic field. The phenomenon results in essentially increase of gain coefficient and opens the possibility of narrow-band amplification frequency tuning in TBRTS in THz range by variation of applied bias voltage.

Terahertz detection by InGaAs HEMTs in quantizing magnetic fields: Relation between magnetoresistance and photovoltaic response

THz detection by plasma wave mechanism in InGaAs HEMTs is studied in high/quantizing magnetic fields regime. The correlation between the photovoltaic response and magnetoresistance is revealed. It allows to explain the nature of strong oscillations observed in the transistor Terahertz photoresponse.

Vertical transport in multiple-wide-quantum-well structures with homogeneous and with large-scale disorder nonhomogeneous interfaces

The time-dependent approach is applied to the description of resonant tunnelling vertical transport accompanied by LO-phonon scattering in asymmetric double-quantum-well systems both with ideal flat and large-scale disorder interfaces. The square-law dependence of dissipative resonant tunnelling rate on the value of coupling matrix element V in the structures with flat interfaces has been found to be radically different from the linear dependence tunnelling rates on V in the structures with nonhomogeneous interfaces. As a result a substantial decrease in the effective tunnelling time in the case of nonhomogeneous interfaces is exhibited in compare with the case of structures with an ideal flat interface, particularly in weakly coupled structures. The physical reasons for the diversity of the functional dependence are discussed.