Mechanism of electron localization in a quantum wire

We show that quasi-bound electron states are formed in a quantum wire as a result of electron backscattering in the transition regions between the wire and the electron reservoirs, to which the wire is coupled. The backscattering mechanism is caused by electron density oscillations arising even in smooth transitions due to the reflection of electrons not transmitting through the wire. The quasi-bound states reveal themselves in resonances of the electron transmission probability through the wire. The calculations were carried out within the Hartree-Fock approximation using quasiclassic wavefunctions.Comment: 7 pages, IOP style, 4 figures, typos corrected, published versio

Temperature-dependent quantum electron transport in 2D point contact

We consider a transmission of electrons through a two-dimensional ballistic point contact in the low-conductance regime below the 0.7-anomaly. The scattering of electrons by Friedel oscillations of charge density results in a contribution to the conductance proportional to the temperature. The sign of this linear term depends on the range of the electron-electron interaction and appears to be negative for the relevant experimental parameters.Comment: 10 pages, 5 figure

Intersubband Electron Interaction in 1D-2D Junctions

We have shown that the electron transport through junctions of one-dimensional and two-dimensional systems, as well as through quantum point contacts, is considerably affected by the interaction of electrons of different subbands. The interaction mechanism is caused by Friedel oscillations, which are produced by electrons of the closed subbands even in smooth junctions. Because of the interaction with these oscillations, electrons of the open subbands experience a backscattering. The electron reflection coefficient, which describes the backscattering, has a sharp peak at the energy equal to the Fermi energy and may be as high as about 0.1. This result allows one to explain a number of available experimental facts.Comment: 5 pages, 3 figure

Electron transport in a quantum wire with realistic Coulomb interaction

Electron transport in a quantum wire with leads is investigated with actual Coulomb interaction taken into account. The latter includes both the direct interaction of electrons with each other and their interaction via the image charges induced in the leads. Exact analytical solution of the problem is found with the use of the bosonization technique for one-dimensional electrons and three-dimensional Poisson equation for the electric field. The Coulomb interaction is shown to change significantly the electron density distribution along the wire as compared with the Luttinger liquid model with short-range interactions. In DC and low frequency regimes, the Coulomb interaction causes the charge density to increase strongly in the vicinity of the contacts with the leads. The quantum wire impedance shows an oscillating behavior versus the frequency caused by the resonances of the charge waves. The Coulomb interaction produces a frequency dependent renormalization of the charge wave velocity.Comment: 10 two-colomn revtex pages, 6 postscript figures; one figure changed, some typos corrected, to be published in Phys.Rev.

Nonlinear effects in microwave photoconductivity of two-dimensional electron systems

We present a model for microwave photoconductivity of two-dimensional electron systems in a magnetic field which describes the effects of strong microwave and steady-state electric fields. Using this model, we derive an analytical formula for the photoconductivity associated with photon- and multi-photon-assisted impurity scattering as a function of the frequency and power of microwave radiation. According to the developed model, the microwave conductivity is an oscillatory function of the frequency of microwave radiation and the cyclotron frequency which turns zero at the cyclotron resonance and its harmonics. It exhibits maxima and minima (with absolute negative conductivity) at the microwave frequencies somewhat different from the resonant frequencies. The calculated power dependence of the amplitude of the microwave photoconductivity oscillations exhibits pronounced sublinear behavior similar to a logarithmic function. The height of the microwave photoconductivity maxima and the depth of its minima are nonmonotonic functions of the electric field. It is pointed to the possibility of a strong widening of the maxima and minima due to a strong sensitivity of their parameters on the electric field and the presence of strong long-range electric-field fluctuations. The obtained dependences are consistent with the results of the experimental observations.Comment: 9 pages, 6 figures Labeling of the curves in Fig.3 correcte

MOCVD growth and characterisation of ZnS/ZnSe distributed Bragg reflectors and ZnCdSe/ZnSe heterostructures for green VCSEL

High reflectivity ZnS/ZnSe distributed Bragg reflectors (DBR) have been grown on GaAs(100) substrates using metallorganic chemical vapour deposition technique. It was found that the surface roughness, which limits the ZnS/ZnSe DBR mirror reflectivity, may be reduced using the interruption of chalcogen-contained flow before each successive layer growth. The DBR mirrors have been obtained with reflectivity as high as 99% and 94% at the wavelengths of 478 nm and 520 nm, respectively. The ZnCdSe/ZnSe QW structure grown on the ZnS/ZnSe DBR mirror manifests cathodoluminescence at room temperature whose intensity is an order of magnitude less than that of the similar structure grown on ZnSe buffer. Large lattice mismatch between ZnS and ZnSe layers results in high density of defects in ZnCdSe/ZnSe QW structures grown on. the DBR