Room temperature photoreflectance (PR) spectroscopy has been utilized to study the effect of electric fields on the optical properties of GaAs/AlGaAs coupled double quantum wells (CDQWs). The behavior of optical transitions when subjected to electric fields ranging from 0 to 2×105V/cm, was found to be similar to that observed at low temperatures using photoluminescence excitation spectroscopy. Large shifts in the energies of spatially indirect transitions were observed when the CDQW was subjected to modest bias voltages.

We have investigated the carrier concentration effect on AlGaAs/GaAs superlattice mixing enhanced by Si doping. The Al0.01Ga0.99As/GaAs superlattice sample with various Si-doping concentrations was grown by molecular beam epitaxy (MBE). Secondary ion mass spectrometry (SIMS) and carrier concentration profiling were used to characterize the Al diffusion and the free-carrier concentration profiles. The Al diffusion coefficients at 800 C show a high power dependence on the free carrier concentration which is not consistent with a Ga vacancy diffusion mechanism. A possible explanation can be provided by a mechanism based on a Si pair diffusion model.

Variable Angle of incidence Spectroscopic Ellipsometry (VASE) is a sensitive, nondestructive method of determining optical constants, layer thicknesses, alloy compositions and other parameters. We model the VASE data for a sample containing a 20 period Al0 5Ga0 5As-GaAs superlattice, to obtain the effective index of refraction (n) and e tinction coefficient (k) of the superlattice layer. The room temperature VASE spectra contain strong, sharp features at the e-hh(1), e-lh(1) and e-hh(2) excitonic tran-sition energies. In addition, VASE was used to characterize more compli-cated layered structures, which also contained superlattices.

Raman spectra of the GaAs-AlAs superlattice grown by molecular beam epi-taxy along the [110] direction were studied for the first time. The spectra were compared with spectra of the [100] superlattice and differences due to different crystallographic structure were analyzed. It was found that the energies of folded acoustical modes are higher in the [110] superlattice due to higher sound velocity in the [110] direction. Confined transverse optical phonons were a dominant feature of the spectrum of the [110] superlattice which allowed observation of the folding of transverse optical phonons. Stronger intensity of interface modes and lower intensity of folded acousti-cal modes in the [110] superlattice indicated that the quality of the layer interfaces was worse than in the [100] superlattice.

Photoluminescence measurements of Be-doped GaAs, grown by molecular beam epitaxy, were carried out at low temperature as a function of acceptor concentration. Results revealed that besides the well-defined emission, [g-g], which is exclusively relevant to acceptor impurities, an additional specific emission, temporarily denoted by [g-g]α is formed near the band-edge, when the concentration of acceptors exceeds 1×1019 cm−3:. From the viewpoint of application it was suggested that also in case of acceptors, photoluminescence spectra can be practically used for the precise determina-tion the acceptor concentration.

The carbon concentrations in GaAs and AIGaAs grown by Molecular Beam Epitaxy (MBE) have been studied when a graphite generated dimeric arsenic species and a standard tetramer arsenic species are used as the group-V source. Photoluminescence and Van der Pauw-Hall measurements have been made to examine the material quality in reference to which arsenic species is used for film growth. Results indicate that a graphite crucible arrangement for the thermal cracking of As4 produces significant carbon contamination and is unacceptable for the MBE growth of GaAs and AlGaAs.

The interface recombination velocity at n+ GaAs/n GaAs and n+ Al15 Ga85 As/n GaAs are reported for various dopings. It is seen that with an n+ GaAs cap layer it is possible to reduce the interface recombination velocity to ∼ 4.4 × 103 cm/s. This can be further reduced by employing an AlGaAs cap, due to the increased barrier caused by the valence band discontinuity.

Triethylarsenic was successfully used as a substitute for arsine in the atmospheric pressure OMCVD growth of GaAs epilayers. N-type GaAs films were produced at V/III ratios of 14–45 and growth temperatures of 560–590°C. The highest quality epilayers obtained were grown at temperatures of 560–570°C and V/Ill ratios of 23–27, with the best films exhibiting net carrier concentrations and 77K mobilities of ∼1015 cm−3 and ∼14,000cm2/V-s, respectively. All of the films grown using Et3As were found to be contaminated with carbon, which appears to result from an inherent decomposition mechanism of the Et3As reagent.

A fundamental understanding of the channel-buffer (substrate) interface is obtained from the experimental and theoretical investigation of long channel GaAs MESFET's fabricated by molecular beam epitaxy (MBE). The threshold voltage dependence on the semiconductor crystal lattice temperature indicates that the steady-state carrier trapping and accumulation of negative charge in donor-like states at the channel-buffer (substrate) interface play a detrimental role both in the linear and saturated regimes of device operation. The variations of the threshold voltage and gate capacitance with substrate bias are consistent with each other and suggest that significant reduction in the channel charge occurs with increased reverse bias on the substrate. The threshold voltage is found to decrease significantly as the sample temperature is increased both in the linear and saturated regimes of device operation.

This work reports a detailed study of the bound exciton recombination energy measured by low temperature (7K) photoluminescence, as a function of the relative lattice mismatch between the InGaAs epitaxial layers and the substrate measured by double crystal x-ray diffraction. Nominally undoped lμm and 2μm epitaxial layers of InGaAs/InP were grown by metal organic chemical vapor deposition (MOCVD). All InGaAs epitaxial layers used in this study show a single narrow rocking curve peak (FWHM < 25 arc-sec) and only a single narrow PL peak (FWHM < 2.5 meV). Near lattice match the PL energy varies linearly with the mismatch but the absolute value of the PL energy at lattice match is a function of the type of substrate used.

Mn-doped In1−x GaxAsyP1−y epilayers lattice matched to InP substrate have been grown by the liquid phase electroepitaxial (LPEE) technique. The variation of growth velocity of the epilayers with current density and the doping characteristics of Mn in the epilayer has been studied. The temperature dependence of the hole concentration and the mobility has been analysed to determine the donor and acceptor densities, thermal activation energy of the level associated with Mn and the dominant scattering mechanisms that limit the hole mobility. The photoluminescence spectra of the doped epilayers are examined at 10K as a function of the excitation level.

Epitaxical growth rates depend strongly on the crystalline orientations of substrate surfaces. Multilayer growth on pre-patterned substrates with various crystal facets exposed results in a large variation of layer thicknesses in the lateral direction. This lateral definition can be used in device applications. Alternating layers of GaAs and AIGaAs were grown by molecular beam epitaxy on (100) GaAs substrates patterned with grooves and ridges along the [01T] and [011] directions by chemical etching. The results were analyzed with transmission electron microscopy using vertical cross-section techniques. Examples of using this method to fabricate ridges with tips of atomic sharpness and quantum-well lasers are presented.

We present a magnetoreflectivity study of the excitons in MBE grown Zn1−xFexSe crystals for x=0.017, 0.027 and 0.043. The excitonic spinsplitting was studied as function of magnetic field in both the Faraday and Voigt geometries. The exchange integrals were determined from the conduction and valence band spin-splittings. The exciton spin-splitting was also studied as function of temperature. This study yielded the value of the energy spacing of the Fe++ states and also verified that Zn1−xFexSe is a Van Vleck paramagnet.

Covalent metallic superlattices and isoelectronic alloys consist of ordered layers of, for example, Si/AlP, Ge/GaAs, and Si/Sb,etc. Depending on design, wide range of electrical properties can result. The covalent, metallic and ionic radii play a crucial role in the stoichiometry of epitaxial systems.

A 900A single crystalline GaAs film deposited by molecular beam epitaxy (MBE) on a silicon crystal cut 4.1° from (001) surface was characterized with X-ray diffraction measurements of the mosaic spread, particle size and strain distribution, and lattice parameter. The GaAs film had a larger mosaic spread in the direction of the steps of the silicon surface and coherent particle sizes of about 900 Å compared to the estimated film thickness of approximately 1000 Å. Superlattice reflections gave an ordered domain size of about 330 Å. There is a residual strain gradient in the film which is nearly linear with the lattice constant differing by about 0.044 Å between the surface of the film and its interface with the silicon substrate. Lattice parameter measurements indicate a small expansion of 0.13% perpendicular to the plane of the film.

We report a detailed study using photoluminescence and photoluminescence excitation of MOCVD GaAs grown directly on Si substrates. Temperature variation and selective excitation allow reliable assignment of spectral features. This assignment permits measurements of strain and strain uniformity, identification of impurities, and assessment of general materials quality. In 2–5μm thick layers similar spectra are observed with little variation from substrate character. Most samples show one of the two split valence band features plus defect recombination, always including carbon. Strain uniformity varies widely and correlates with substrate thickness. The range of spectra observed from a variety of samples, and guidelines for interpretation of nonresonantly excited spectra will be discussed.

Interfacial reactions between Ni and GaAs have been studied using bulk diffusion couples of Ni(∼0.5mm thick)/GaAs and thin-film Ni (∼40nm) on GaAs (100) in addition to phase diagram determination at 600° C. On the basis of the phase diagram and the bulk diffusion couples, the ternary phase which forms first in the thin-film couples is Ni3 GaAs. Thinfilm studies show that the epitaxial growth of equilibrium contact phases, i.e., NiAs and β-GaNi, on a GaAs (100) substrate is possible.

Modifications in the course of reaction between Co thin films and single crystal GaAs substrate due to the addition of a Ge film either on top or below the metal layer have been studied. The microstructure and phase formation for the systems: Co/GaAs, Co/Ge/GaAs, and Ge/Co/GaAs have been studied by Auger electron spectroscopy, transmission electron microscopy and X-ray diffraction.

The stability of Ag Schottky contacts on GaAs after voltage and current stressing has been investigated. The barrier height and its stability against voltage and current stressing were found to depend on the diode fabrication method (metal deposition onto either air-exposed or ultrahigh vacuum cleaved (UHV) substrates). The barrier height of Ag diodes formed on air exposed surfaces is 0.96 eV, and a significant decrease of 70 meV was found upon exposure to voltage and current stressing. In contrast, the barrier height of Ag diode formed on UHV cleaved samples is 0.89 eV, and no significant change was found upon exposure to stressing. The structure of the contacts was studied by transmission electron microscopy. Ag deposited on UHV cleaved substrates shows an epitaxial relationship to GaAs and atomically flat interfaces. Exposure to air before the metal deposition led to nonuniform reactions and compound formation at the interface as compared to UHV samples. After current stressing, void formation and electromigration of Ag was observed in the air-exposed contacts. Ag contacts formed on UHV-cleaved GaAs (110) were stable during current stressing.

Reaction between Rhodium films and n-type GaAs in the temperature range of 300° to 700°C has been examined using the TEM to look at the interface and phases present. The reaction between Rh and GaAs produces a layered structure of Rh/RhGa/RhAs2/GaAs based on RBS and TEM. Above 300°C, the RhGa phase has an orientation relationship of [011]RhGa // [100]GaAs. In cross-section, an interpenetrated layered structure was observed with equiaxed RhGa above columnar grains of RhAs2. Rhodium is the moving species as suggested by voids at the Rh/reacted layer interface. The interface between the reacted layer and GaAs was smooth at 450° and 20 minutes of annealing but showed 10 nm periodic penetrations when annealed at 400° for 90 minutes. Interface roughness may influence the low barrier height reported for the Rh Schottky diode annealed at 400°.