The effects of In and Sb on the concentration of electron traps in MBE grown n-type GaAs are investigated. Two traps, labeled M3 and M6, dominate the DLTS spectrum. It is observed that at growth temperatures of 500 and 550° C their concentrations can be reduced by up to two orders of magnitude by the introduction of a few atomic percent of either In or Sb. The percent In or Sb producing the lowest trap concentrations decreases with increasing substrate temperature and thus for a substrate growth temperature of 600° C no additional improvement in the deep trap concentration is observed.

An indium-free substrate mounting technique was developed for a 190-mm diameter substrate holder on which three 3-inch GaAs substrates are mounted. Reduction of the heat conduction between the substrates and the holder kept the temperature variation in the substrate within ±5° C. Highly uniform epitaxial layers were grown with low residual impurity concentrations using this technique. The variations in layer thickness and carrier concentration of Si-doped GaAs and AlGaAs epitaxial layers were within ±1% over the substrate holder. High mobility of a two-dimensional electron gas in a selectively doped GaAs/N-AlGaAs heterostructure was obtained uniformly over three 3-inch wafers. Since the holder was designed to hold the wafers without stress, no stress-related degradation of the surface morphology was observed.

We report our recent investigations of a new structure formed by b-doping the barrier of an AlGaAs/GaAs heterostructure. In this new structure we have observed both a mobility of 1.9×lO6cm2/Vsec and the fractional quantum hall effect. We compare low temperature mobilities and densities achieved with the δ-doped heterostructure with corresponding high values reported in the literature for the homogeneously- doped heterostructure. We show that systematic enhancements in both density and mobility occur in the b-doped heterostructure. By δ-doping both barriers of a quantum well we have also achieved electron concentrations of 4×1012cm -2 in the well.

InP/GalnAs/InP quantum well structures have been grown using atmospheric pressure organometallic vapor phase epitaxy (AP-OMVPE). The optimum conditions for growth of extremely abrupt interfaces were studied. The optimum orientation was exactly (100). The growth had to be interrupted for 40 seconds at the first interface and 2 minutes at the 2nd interface to obtain the most abrupt interfaces. The narrowest photoluminescence half widths were obtained at the lowest values (31) of V/III ratio in the input vapor phase. These growth conditions allow the growth of wells as thin as <10Å with photoluminescence (PL) spectra consisting of doublets or triplets. The extremely narrow peaks correspond to regions of the quantum well differing in thickness by a single monolayer. The energy separations of the neighboring peaks are found to increase with decreasing well width until, at a thickness of approximately 12 Å, the separation begins to decrease rapidly with decreasing well width. The exciton binding energies in the quantum wells have also been measured using thermally modulated PL. The binding energy is found to increase with decreasing well width until a maximum value of approximately 17 meV is measured for a nominal well width of approximately 13 Å. For thinner wells the exciton binding energy is found to decrease with decreasing well width.

The kinetics of atomic layer epitaxy (ALE) of GaAs utilizing trimethylgallium and arsine are described. The results show that saturated monolayer growth can be achieved-in the temperature range 445°C -485°C and that high quality materials can be grown.. Hybrid A1GaAs/GaAs heterostructures have been grown utilizing ALE for the active regions and conventional metalorganic chemical vapor deposition (MOCVD) for the confining regions that yield high quality quantum wells and low threshold quantum well lasers.

Fe-doped semi-insulating AlGalnAs grown by liquid phase epitaxy has been studied and compared to Fe-doped GalnAsP. It has been found that semiinsulating AlGalnAs is easier to obtain than semi-insulating GalnAsP, because of its high iron distribution coeficient. The high resistivity of 1×109 ohm-cm has been obtained for Al0.481n0.52 As grown at 750°C. The activation energy of the Fe acceptor level in the AlGalnAs system has also been studied.

X-ray topography(XRT) and EBIC have been used to study the generation of misfit dislocations in strained layer structures. Two structures studied were GaAs1−yPy(y=0.15) film and SLS consisting of InxGa1−xAs(x=0.08) and GaAs1−y Py(y=0.16) layers. XRT and EBIC techniques gave consistent results for the behavior of dislocations. The value of the critical thickness for generation of misfit dislocations in the former was found to be few times larger than that in the latter. EBIC image showed that a SLS lattice matched to the substrate is effective in reducing defects originating from the substrate.

MeV H+ and He+ ion channelling has been used to characterise the post annealing, residual ion implantation damage in silicon. The observed energy dependence of direct scattering peaks agrees with theoretical predictions for direct scattering on dislocations. Similar peaks are observed in the channelling spectrum from the hetero-epitaxial structure In0.3Ga0.7 As on GaAs and are also interpreted as direct scattering on interfacial dislocations. The sensitivity for dislocation detection by this technique is about 1×105 cm−1 therefore, when high dislocation densities are expected, it is suggested that direct scattering on dislocations should be included in the analysis of channelling data.

For thin (Ga1−xInx)As films on GaAs (100) substrates we have measured the phonon frequencies (Raninn technique) and the strains (x-ray rocking curve technique). The films range from perfect epitaxial (the thinner films) to those that have relaxed by different amounts (thicker films). Using the measured strains and the phonon deformation constants, the strain-induced frequency shift was calculated for each sample. From the measurements and calculation, we find that the frequency shifts due to strain give equivalent bulk phonon frequencies that are in good agreement with each other. This indicates that the Raman technique can be used for in-situ monitoring of the growth process.

Energy relaxation rates for light holes in InGaAs/GaAs strained layer quantum wells are measured. Two techniques were used to measure light hole temperatures as a function of power dissipated in the hole gas. For Th < 20K, Shubnikov-de Haas oscillations were used and for Th> 20K, a photoluminescence technique was employed.

Strained-layer heterojunctions and superlattices have recently shown tremendous potential for device applications because of their flexibility for tailoring the electronic band structure. We present a theoretical model to predict the band offsets at both lattice-matched and pseudomorphic strained-layer interfaces. The theory is based on the local-density- functional pseudopotential formalism, and the “model solid approach” of Van de Walle and Martin. The results can be most simply expressed in terms of an “absolute” energy level for each semiconductor, and deformation potentials that describe the effects of strain on the electronic bands. The model predicts reliable values for the experimentally observed lineups in Si/Ge, GaAs/InAs, and ZnSe/ZnS systems, and can be used to ex-plore which combinations of materials and configurations of the strains will lead to the desired electronic properties.

We present a detailed experimental study of the influence of electric fields on exciton states in a GaAs/AlGaAs coupled double quantum well structure and discuss the advantages of using this novel structure. The coupling of electronic states in the two quantum wells, due to the narrowness of the barrier between them, leads to an enhancement of the quantum-confined Stark effect (by as much as five times that of the single quantum well case). From the measured energies of the exciton transitions, splittings of the levels in a coupled double quantum well structure were derived without recourse to a theoretical model.

Heteroepitaxial ZnSe grown by molecular beam epitaxy (MBE) has been characterized using low temperature photoluminescence (PL) and reflectance. Excitonic PL linewidths of thick (relaxed) ZnSe layers are>1.4 meV, and depend little on the type of substrate or buffer layer used (e.g. GaAs or AlAs). In contrast, thin (pseudomorphic) ZnSe layers on AlAs buffer layers of moderate thickness are found to exhibit by far the sharpest (FWHM=0.22-0.37 meV) excitonic features ever observed for heteroepitaxial ZnSe grown by any technique. A tentative explanation for this result is that step-grading the lattice constant (by the AlAs buffer layer) has eliminated the crystal defects which produce localized strain fields that inhomogeneously broaden the peaks in ZnSe/GaAs. Acceptor-related PL peaks are discussed, and the first discrete donor-acceptor pair line spectrum in heteroepitaxial ZnSe is reported.

Transmission electron microscopy (TEM) and transmission electron diffraction (TED) studies have shown the presence of long range CuPt-type cationic ordering 4n GaInP grown by MOCVD on (001) GaAs. Domains regions (on order of 104nm2) exhibit a double periodicity along the [111] and [110] directions.

The ordered structure in a (100) GaAs0.5 Sb0.5 epilayer grown by molecular beam epitaxy has been studied by transmission electron microscopy. Domain structures are observed in dark field images of superstructure reflections. The ordered structure is derived by the analysis of diffraction patterns taken from single domains. The ordered structure is described as an alternate stacking of As and Sb planes in the <111> direction of the FCC sublattice. The alternate stacking of As and Sb plane is directly observed by high resolution electron microscopy.

Various thicknesses of AlGaAs are grown on GaAs substrates by MOCVD. Low temperature photoluminescence of the substrate is observed even for layers of AlGaAs 24μm thick. Direct excitation by the 488.0 nm pumping radiation and excitation by reradiation from the AlGaAs are eliminated as causes. From photoluminescence and EBIC studies, evidence is given to show that the substrate luminescence is caused by a much larger than expected electron diffusion length. A small trace of GaAs luminescence may be due to alloy segregation in the AlGaAs films themselves.