Communications in Theoretical Physics
Effects of interface defects on electronic states in quantum wells (QWs) are investigated theoretically by introducing a coordinate transformation that transforms QWs with defective interfaces to those with planar interfaces plus an effective potential associated with interface defects. The interface defects are idealized as a cylindrical hollow protruding into the barrier materials on one of the interfaces. Electronic ground state energies are calculated variationally as functions of the defect lateral sizes. For GaAs-Ga1-xAlxAs QWs with the well width d less than 150 angstrom, the changes in electronic energies due to interface defects will produce sizable effects on optical experiments, such as broadenings of excitation spectra of QWs. But our calculation predicts smaller spectrum broadenings than those predicated by the previous theory for the same interface disorder.
关键词:
optical characterization;roughness;disorder;growth
Chinese Physics Letters
With the help of a set of exact closed-form solutions to the stationary Gross-Pitaevskii equation, we comprehensively investigate Landau and dynamical instabilities of a Bose-Einstein condensate in a periodic array of quantum wells. In the tight-binding limit, the analytical expressions for both Landau and dynamical instabilities are obtained in terms of the compressibility and effective mass of the BEC system. Then the stability phase diagrams are shown to be similar to the one in the case of the sinusoidal optical lattice.
关键词:
phase-transition;optical lattices;mott-insulator;superfluid;dynamics
Journal of Physics-Condensed Matter
With both longitudinal optical (LO) and surface optical (SO) modes included, the influence of electron-phonon interactions on the quantum confined Stark effect in quantum wells is investigated by means of the variational technique. For an infinite GaAs-GaAlAs quantum well with a shallow donor located at its centre and subjected to an external electric field, the energy shifts of a conduction electron are calculated approximately. It is found that the presence of an ionized impurity decreases the energy shift. The LO mode and SO mode effect will give significant corrections to the Stark energy shift individually and their influences on the shift are just opposed.
关键词:
electric-field dependence;impurity states;optical-absorption;excitons;slab
Physica B-Condensed Matter
The longitudinal transported properties of the one-dimensional (1D) multilayer system - Canter fractal multiquantum wells (MQWs) - have been studied from the tunneling point of view. A transfer matrix technique is introduced for the calculation of the transmission coefficient. Some new results have been obtained. It is found that its tunneling spectrum is more complex and distinct than that of the periodic MQWs. High peak-valley ratios are obtained in the tunneling spectra of the well-width-modulated Canter fractal MQWs. There is a continuous wide band of resonant tunneling through the Canter fractal MQWs.
关键词:
multi-quantum wells;tunneling;one-dimensional multilayer;transmission
Physical Review B
The effects of an image potential on the electronic and hydrogenic impurity states in AlAs/GaAs/AlAs quantum wells are calculated by using variational solutions to the effective-mass equation. The results we have obtained show that when the image potential is added the variations of electronic state energy levels and impurity binding energies are significant, especially when the width of the quantum well becomes narrow. The results also show that the effects of the impurity-ion image potential on impurity binding energies are much larger than those of the electron image potential.
关键词:
2 orthogonal surfaces;binding-energies;vicinity
Acta Chimica Sinica
Passive film formed on 304 stainless steel in 2.5 mol/L H2SO4 solution by using alternating voltage (A. V.) passivation have been investigated by measuring capacitance and photoelectrochemical parameters. The investigation of the effect of measure frequency on the slope of Mott-Schottky curve has been carried out. The photoelectrochemical measurements were consistent with the capacitance measurement. Analysis of the experimental results showed that the passive film formed 304 stainless steel by using A. V. passivation exhibits semiconducting properties. Using the simple model of semiconductor rather than the multi-donor level model can explain satisfactorily the semiconducting behavior of the film formed on 304 stainless steel by using A.V. passivation.
关键词:
A. V. passivation;passive film;semiconducting properties;stainless;steel;model;electrodes
Journal of Physics B-Atomic Molecular and Optical Physics
A set of exact closed-form Bloch-state solutions to the stationary Gross-Pitaevskii equation are obtained for a Bose-Einstein condensate in a one-dimensional periodic array of quantum wells, i.e. a square-well periodic potential. We use these exact solutions to comprehensively study the Bloch band, the compressibility, effective mass and the speed of sound as functions of both the potential depth and interatomic interaction. According to our study, a periodic array of quantum wells is more analytically tractable than the sinusoidal potential and allows an easier experimental realization than the Kronig-Penney potential, therefore providing a useful theoretical model for understanding Bose-Einstein condensates in a periodic potential.
关键词:
optical lattices;sound-propagation;gas;dynamics;atoms;bands
Physical Review B
Effects of interface defects on polaron states in GaAs-Ga(1-x)Al(x)As quantum wells (QW's) are investigated theoretically by introducing a coordinate transformation that transforms QW's with defect interfaces to those with planar interfaces with an effective potential associated with the interface defects. The interface defects are idealized as an infinite track or a cylindrical hollow protruding into the barrier material on one of the interfaces. Polaron ground-state energies are calculated variationally as functions of the defect lateral sizes. For GaAs-Ga(1-x)Al(x)As QW's with well width d less than 150 angstrom, the changes in polaron ground-state energies due to interface defects are expected to lead to sizable effects on optical experiments, such as broadening of the luminescence, absorption, and excitation spectra of GaAs-Ga(1-x)Al(x)As QW's but our calculation predicts smaller spectrum broadenings than those predicated by a previous theory for the same interface disorder. Changes in polaron self-energies and polaron effective masses caused by interface defects are negligible for materials with weak electron-LO-phonon interactions, such as GaAs for which the Frohlich coupling constant alpha-LO is less than 0.1. Effects of interface defects on exciton states in QW's are discussed qualitatively.
关键词:
2 dimensions;optical characterization;cyclotron-resonance;electric-field;ground-state;localization;energy;disorder
Communications in Theoretical Physics
With both LO and SO modes being taken into account, the influence of electron-phonon interaction on QCSE of a bound polaron in a finite quantum well (QW) is investigated by means of the perturbation-variation method. It is found that the presence of an ionized impurity decreases the energy shift and weakens the effect of a finite barrier height. LO and SO mode effects will give significant corrections to the Stark energy shift individually and their influences on the shift just are contrary.
关键词:
electric-field;optical-absorption;electroabsorption;gaas;slab
