Search

We have studied the exciton states in vertically stacked self-assembled quantum disks within the effective mass approximation. The energy spectrum of the elect ron and hole is calculated using the transfer matrix formalism in the adiabatic approximation. The Coulomb interaction between the electron and the hole is trea ted accurately by the direct diagonalization of the Hamiltonian matrix. The effe ct of the vertical alignment of the disks on the ground energy of heavy- and li ght-hole exciton is presented and discussed. The binding energy is discussed in terms of the probability of the ground wave function. The ground energy of heav y- and light-hole excitons as a function of the magnetic field is presented an d the effect of the disk size (the radius of disks) on the exciton energy is dis cussed.

Photoluminescence study of (GaAs1-xSbx/InyG a1-yAs)/GaAs bilayer quantum wells (BQWs) grown by molecular beam epitaxy (MBE) were carried out. Temperature and excitation power dependent photoluminescence (PL) s tudy indicated that the band alignment of the BQWs is type - Ⅱ. The origin of the double-peak luminescence was discussed. Under optimized growth conditions, t he PL emission wavelength from the BQWs has been extend up to 131 μm with a s ingle peak at room temperature.

We have calculated the bond distributions and atom positions of GaAs/GalnNAsSb superlattices using Keating's semiempirical valence force field (VFF) model and Monte Carlo simulation. The electronic structures of the superlattices are calculated using folded spectrum method (FSM) combined with an empirical pseudopotential (EP) proposed by Williamson et al.. The effects of N and Sb on superlattice energy levels are discussed. We find that the deterioration of the optical properties induced by N can be explained by the localization of the conduction-band states around the N atom. The electron and hole effective masses of the superlattices are calculated and compared with the effective masses of the bulk GaAs and GaInAs.

InAs self-assembled quantum dots(QDs) covered by 3-nm-thick InxGa1-xAs(0 less than or equal tox less than or equal to0.3) capping layer have been grown on GaAs(100) substrate. Transmission electron microscopy shows that InGaAs layer reduces the strain in the InAs islands,and atomic force microscopy evidences the deposition of InGaAs on the top of InAs islands when x = 0.3.The significant redshift of the photoluminescence (PL) peak energy and the reduction of PL linewidth of InAs quantum dots covered by InGaAs are observed. In addition,InGaAs overgrowth layer suppresses the temperature sensitivity of PL peak energy. Based on our analysis, the strain-reduction and the size distribution of the InAs QDs are the main cause of the redshift and temperature insensitivity of the PL respectively.

Uniform triangular dots (TDs) and ridge dots (RDs) structures are grown by moleculat beam epitaxy (MBE) on square mesa and hole patterned (311)A substrates. The surface morphology and cross-sectional characterization of the dot structures investigated by atomic force microscopy(AFM) and scanning electron microscopy(SEM) show that the TDs and RDs structures are formed on the hole and mesa patterned areas during the growth. TDs are one-side pinch-off structure evaluated between the holes with highly uniform tips along ［233］ direction, and the RDs two-side pinch-off structure accomplished on the mesa with ordered two opposite tips, respectively. The AFM line-scan height profiles of the dots structures indicate that the TDs and RDs structures are dominated by the Ga adatoms preferential migration from symmetric (331)A side walls of the mesa and holes to the bottom region to develop the triangular shaped tips structure, while the facet orientation of the tips is determined by the original side walls orientation of the mesa and hole to lead to form uniform pinch-off arrays. The cathode luminescense measurements reveal that the line,dot,ring-like lateral variations of quantum well confinement energies are formed in the regions of the TDs and RDs structures. These unique growth phenomenon provides a good possibility to realize three-dimensional quantum confinement structures by using MBE growth on (311)A substrates with much smaller length scale of patterning.

The structures of the strained InGaAs/GaAs ridge quantum wires(QWRs) were proposed and the samples fabricated by MBE growth on patterned substrate. High resolution scanning electron microscope (SEM) studies showed that these ridge structures were formed with (001) top and (113) side faces.The photoluminescence(PL) measurements indicated that the lateral quantum confinement effects of the ridge-QWRs caused the quantum confined energy a 10meV blue-shift, which agreed with the approximate calculations for the strained ridge-QWR structure using Kronig-Penney model. This strainedridge-QWRs consisted of three aspects of lateral confinement effects.Firstly the thickness of ridge quantum wells on the ridge top was larger than that on the side surfaces;Secondly the indium concentrations on the ridge-top region was higher than that on the side region;Thirdly the strain effects led to a larger energy gaps in side (113) plane than that in the (001) ridge top.The above three factors were cooperated to enhance the confinement effects on the lateral motion of carriers in strained ridge QWRs.