Structural ordering and interface morphology in symmetrically strained (GaIn)As/Ga(PAs) superlattices grown on off-oriented GaAs(100)

In this work we investigate the structural properties of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of x-ray diffraction, reciprocal-space mapping, and x-ray reflectivity. The multilayers were grown by metalorganic vapor-phase epitaxy on (001) GaAs substrates intentionally off-oriented towards one of the nearest [110] directions. High-resolution triple-crystal reciprocal-space maps recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction clearly show a double periodicity of the x-ray peak intensity that can be ascribed to a lateral and a vertical periodicity occurring parallel and perpendicular to the growth surface. Moreover, from the intensity modulation of the satellite peaks, a lateral-strain gradient within the epilayer unit cell is found, varying from a tensile to a compressive strain. Thus, the substrate off-orientation promotes a lateral modulation of the layer thickness (ordered interface roughness) and of the lattice strain, giving rise to laterally ordered macrosteps. In this respect, contour maps of the specular reflected beam in the vicinity of the (000) reciprocal lattice point were recorded in order to inspect the vertical and lateral interface roughness correlation, A semiquantitative analysis of our results shows that the interface morphology and roughness is greatly influenced by the off-orientation angle and the lateral strain distribution. Two mean spatial wavelengths can be determined, one corresponding exactly to the macrostep periodicity and the other indicating a further interface waviness along the macrosteps. The same spatial periodicities were found on the surface by atomic-force-microscopy images confirming the x-ray results and revealing a strong vertical correlation of the interfaces up to the outer surface.

Effects of point defects on lattice parameters of semiconductors

A model for analyzing the correlation between lattice parameters and point defects in semiconductors has been established. The results of this model for analyzing the substitutes in semiconductors are in accordance with those from Vegard's law and experiments. Based on this model, the lattice strains caused by the antisites, the tetrahedral and octahedral single interstitials, and the interstitial couples are analyzed. The superdilation in lattice parameters of GaAs grown at low temperatures by molecular-beam epitaxy can be interpreted by this model, which is in accordance with the experimental results. This model provides a way of analyzing the stoichiometry in bulk and epitaxial compound semiconductors nondestructively.

GSMBE growth and PL investigation of lattice-matched InGaAs/InP quantum wells

Using a home-made gas-source molecular beam epitaxy system, high quality InGaAs quantum wells with different well widths lattice-matched to a (001) InP substrate have been obtained. Sharp and intense peaks for each well can be well resolved in the PL spectra for the sample. For well widths larger than similar to 60 Angstrom, the exciton energies are in good agreement with those of calculation. For wells narrower than 40 Angstrom, our line widths are below the theoretical values of line width broadening due to one monolayer interface fluctuation, showing that the interface fluctuation of our sample is within one monolayer.

Photoluminescence of GaInP under high pressure

Photoluminescence of GaInP under hydrostatic pressure is investigated. The Gamma valley of disordered GaInP shifts sublinearly upwards with respect to the top of the valence band with increasing pressure and this sublinearity is caused by the nonlinear relationship between lattice constant and hydrostatic pressure. The Gamma valleys of ordered GaInP rise more slowly than that of the disordered one and the relationship between the band gap and the pressure can not be explained in the same way. Taking into account the interactions between the Gamma valley and the folded L valleys, as well as, the X valleys, the experimental pressure dependences of the band gap of ordered GaInP epilayers are calculated and fitted quite well using first order perturbation theory. The results indicate that simultaneous ordering along [111] and [100] directions can occur in ordered GaInP. (C) 1996 American Institute of Physics.

Ordering along <111> and <100> directions in GaInP demonstrated by photoluminescence under hydrostatic pressure

Photoluminescence of GaInP epilayers under hydrostatic pressure is investigated. The Gamma valley of disordered GaInP shifts sublinearly upwards with respect to the top of the valence band with increasing pressure and this sublinearity is caused by the nonlinear dependence of lattice constant on the hydrostatic pressure. The Gamma valleys of ordered GaInP epilayers rise slower than that of the disordered one. Considering the interactions between the Gamma valley and folded L and X valleys, the pressure dependence of the band gap of ordered GaInP is calculated and fitted. The results demonstrate that not only ordering along [111] directions but also sometimes simultaneous ordering along [111] and [100] directions can occur in ordered GaInP. (C) 1996 American Institute of Physics.

PHOTOLUMINESCENCE OF ORDERED GA0.5IN0.5P GROWN BY METALORGANIC VAPOR-PHASE EPITAXY

Optical properties of ordered Ga0.5In0.5P epitaxial layers grown by metalorganic vapor phase epitaxy are investigated by photoluminescence (PL) in a temperature range of 10-200 K using excitation power densities between 0.35 W/cm(2) and 20 W/cm(2). It is found that the intensity of the highest-energy PL peak of the ordered Ga0.5In0.5P epilayer decreases first, then increases and finally goes down again with increasing temperature. A model of ordered Ga0.5In0.5P epitaxial layers is proposed, in which the ordered Ga0.5In0.5P epilayer is regarded as a type-II quantum well structure with band-tail states, and the dependence of PL spectra on the temperature and excitation intensity is reasonably explained. (C) 1995 American Institute of Physics.

Transient photocurrent investigation of photo-processes of lattice-matched MQW GaAs/AlxGa1-xAs electrode

Transient photocurrents induced by short light pulses at lattice-matched GaAs/AlxGa1-xAs multiple quantum well (MQW) electrodes were studied as a function of electrode potential. Dual exponential photocurrent decay transients were observed at various potentials. By analysis of the dual exponential decay transients, information on steady state photocurrents (I-s), surface collection of photoexcited minority carriers (G(0)) and lifetimes of surface states (T-s) was obtained. The kinetic behaviors of photoprocesses at illuminated MQW/electrolyte interface were discussed.

Growth of Space Ordered on GaAs（100） Vicinal 1.3μm InAs Quantum Dots Substrates by MOCVD

Space ordered 1.3μm self-assembled InAs QDs are grown on GaAs（100） vicinal substrates by MOCVD. Photoluminescence measurements show that the dots on vicinal substrates have a much higher PL intensity and a narrower FWHM than those of dots on exact substrates, which indicates better material quality. To obtain 1.3μm emissions of InAs QDs, the role of the so called InGaAs strain cap layer （SCL） and the strain buffer layer （SBL） in the strain relaxation process in quantum dots is studied. While the use of SBL results only in a small change of emission wavelength,SCL can extend the QD＇s emission over 1.3μm due to the effective strain reducing effect of SCL.

Iron related emission spectra in InP

This paper presents a detailed PL study of Fe2+ related four zero-phonon(ZP) lines and their related phonon sidebands. Four zero-phonon transitions at approximate to 2800 cm(-1) along with the accompanying phonon sidebands extending down to 2400 cm(-1). There are ta two prominent regions in the phonon sidebands. One is ascribed to coupling to acoustic-type phonons (2700 cm(-1) region), the other is due to coupling to optic-type phonons (2500 cm(-1) region). Beside broad coupling with lattice modes, there are several groups of lines. They are ascribed to resonant modes, impurities induced gap modes and local modes.

Anisotropic strain in (100) ZnSe epilayers grown on lattice mismatched substrates

We show that part of the reflectance difference resonance near the E-0 energy of ZnSe is due to the anisotropic in-plane strain in the ZnSe thin films, as films grown on three distinctly different substrates, GaAs, GaP, and ZnS, all show the resonance at the same energy. Such anisotropic strain induced resonance is predicted and also observed near the E-1/E-1+Delta(1) energies in ZnSe grown on GaAs. The theory also predicts that there should be no resonance due to strain at, the E-0+Delta(0) energy, which is consistent with experiments. The strain anisotropy is rather independent of the ZnSe layer thickness, or whether the film is strain relaxed. For ZnSe films with large lattice mismatch with substrates, the resonance at the E-1/E-1+Delta(1) energies is absent, very likely due to the poor crystalline quality of the 20 nm or so surface layer. (C) 2000 American Vacuum Society. [S0734-211X(00)05604-3].

Formation trends of ordered self-assembled nanoislands on stepped substrates

The growth of ordered self-assembled nanoislands on stepped substrates is studied systematically by kinetic Monte Carlo simulations. As the terrace width is small, the formation of nanoislands is confined in the steps and nanoislands ordered in lines or nanowires can be obtained. The Schwoebel barrier at the step edges has a great influence on the evolution of both the size and space distributions of the islands. When the terrace width is relatively large, self-ordering of nanoislands in the center regions of the terraces happens. An unexpected trend of the nanoisland self-ordering is found as the deposition thickness is larger than 0.2 ML, which can be related to the attractive migrations between nearby islands.