The optical absorption of the band edge of GaSb layers grown on semi-insulating GaAs substrates by the molecular beam epitaxy (MBE) technique is studied as a function of temperature. A free exciton absorption peak at 0.807 eV was observed at 10 K. The free exciton line is observed in either thick samples (5μm thick) or samples with ∼0.1 μm thick AlSb buffer layers. The latter samples suggest that the AlSb buffer layer is very effective in preventing some of the dislocations from propagating into the MBE GaSb layers. The fitting of the band gap of the GaSb layers as a function of temperature gives a Debye temperature different than that of the bulk GaSb calculated from the elastic constants.

For the GaAs buffer layer deposited on Si substrate at 80°C and annealed at 300°C for 10 min, the size of most GaAs islands was observed as ∼ 10 nm but large islands (∼ 40 nm) were also seen. According to the calculation of spacing of moire fringes, large GaAs islands are considered to be rotated about 4 ° with respect to the Si substrate normal. However, for the main GaAs film overgrown on the GaAs buffer layer at 580 °C, moire fringes with the spacing of 5 nm (GaAs film without rotation) completely covered the surface of Si substrate. Misfit dislocations and stacking faults were already formed at the growth stage of buffer layer. Stacking faults and misfit dislocations consisting of Lomer and 60 ° dislocations were observed in GaAs films grown at 580 °C. However, after rapid thermal annealing at 900 °C for 10 sec, only Lomer dislocations with 1/2[110] and 1/2[-110] Burgers vectors were observed.

The temperature and polarization dependence of the optical absorption in ZnGeP2 at two micrometers is reported for the first time over the temperature range from 10K to 300K. The radiation was normally incident upon the face of a cubic sample which contained the c-axis. The absorption of o-rays (E parallel to c), and erays (E perpendicular to c) was determined. It was found that the e-ray absorption coefficient was always significantly larger than the o-ray absorption coefficient and that it had a less significant temperature dependence. For example, the ratio of e-ray to o-ray absorption coefficient was approximately two at 300K and five at 77K. Correspondingly the o-ray absorption coefficients were reduced upon cooling to 77K by a factor of 2.5, while the e-ray absorption coefficients were reduced only slightly (10%-20%). These results indicate that for Type I optical parametric oscillators (OPOs) which use an oray pump beam, that performance may be improved by cooling the crystal.

The gap between the minibands of a conventional superlattice (or between the subbands of a quantum well) can be controlled by introducing potential barriers in its wells. An appropriate choice of the position, the width d, and the height Vd of these barriers, achieved by standard methods, can reduce the energy minibands to the desired values. When these barriers are introduced at the center of the wells of the original structure, the position of the second miniband in energy space changes very little with d and/or Vd whereas that of the first miniband can change by one to two orders of magnitude. This leads to a tuning of the first miniband and of the energy gap between the first two minibands. Similar results are obtained for the case of wells in the barriers and for the tuning of impurity states in a superlattice. Possible applications include infrared photodetectors and tuning of the tunneling current.

The optical and electronic properties of three-dimensional (3D) random GaAs/AlAs superlattices (SLs) has been studied by using a tight-binding Hamiltonian with secondneighbor interactions. We calculate three completely disordered sequences with the probability of GaAs layers being 30%, 50%, and 70%. The higher the GaAs composition, the narrower the indirect gap. An energy-level crossing is found at the bottom of conduction band, which originates from the M-state splitting induced by layer disorder. The localized states over two - four monolayers play an important role in the absorption edge of random SL. The highest absorption intensity of the band-edge transitions in our random models is about eight times stronger than that of short period ordered GaAs/AlAs SL. Our results are in good agreement with some recent photoluminescence measurements.

The band structures of three group-V semimetals As, Sb, and Bi with rhombohedral A7 symmetry are studied using a second-neighbor tight-binding model including spin-orbit interaction with an sp3s* basis. Then the bulk tight-binding parameters are used to investigate the electronic properties of semimetal-semiconductor superlattices made of alternating (111) layers of Sb and GaSb or AlSb. It is found that the band gap can be adjustable depending primarily on the thickness of the Sb layers. An interface state is observed in the region of the gap.

We have grown InAsl-xSbx/Inl-yGayAs strained-layer superlattice (SLS) semiconductors lattice matched to InAs using a variety of conditions by metal-organic chemical vapor deposition. The V/III ratio was varied from 2.5 to 10 at a temperature of 475 °C, at pressures of 200 to 660 torr and growth rates of 3 - 5 A/s and layer thicknesses ranging from 55 to 152 Å. The composition of the InAsSb ternary can be predicted from the input gas molar flow rates using a thermodynamic model. At lower temperatures, the thermodynamic model must be modified to take account of the incomplete decomposition of arsine and trimethylantimony. Diodes have been prepared using Zn as the p-type dopant and undoped SLS as the n-type material. The diode was found to emit at 3.56 μm. These layers have been characterized by optical microscopy, SIMS, x-ray diffraction, and transmission electron diffraction. The optical properties of these SLS's were determined by infrared photoluminescence and absorption measurements.

In this study, we report the optical properties of a variety of compositionally equivalent disordered superlattices in the AlAs/GaAs system. Markedly different signatures are seen in the steady-state optical signatures of a random pseudobinary A10.5Ga0.5As alloy and (AlAs)n(GaAs)4-n superlattices (SLs) where n = 2 (ordered) or n is randomly chosen (disordered). Relative to the properties of the pseudobinary alloy or ordered SL, intense, redshifted, photoluminescence (PL) peaks and broad non-excitonic absorption are observed from disordered (AlAs)n(GaAs)4-n SLs where n is randomly chosen from the sets [0, 1, 2, 3, 4] or [1, 2, 3]. Our observations suggest that a large density of states at energies lower than the compositionally equivalent pseudobinary band gap exist, and including wider wells and barriers may lead strongly localized regions and the onset of quantum effects. Room temperature electroluminescence is also observed from disordered SL pn samples, and the energy, intensity, and efficiency are shown to vary with deposition sequence.

We performed low temperature photocurrent and photoluminescence excitation spectroscopy on tensile and compressively strained GaxIn1-xAs/GaInAsP quantum well layers to determine the band offset of the heterojunction (0.3 <XGa < 0.7). The ratio of the conduction band discontinuity to the heavy hole discontinuity has been obtained from well to barrier transitions and is found to be about 35/65 for gallium contents between 0.4 and 0.6. We obtained the effective heavy hole mass by comparison of PLE transition energies with calculations of the subband levels. We observe that the effective heavy hole mass increases with the gallium content from 0.3 m0 for XGa = 0.31 to about 0.45m0 for XGa = 0.55.

We report a cathodoluminescence spectroscopy study of growth-induced deep levels at GaInP epilayers grown by Molecular Beam Epitaxy under various conditions. This approach allows the identification of deep levels which appear to play an important role in the band to band radiative recombination efficiency of these GaInP films. Control of these electronic defects is crucial for the performance of visible optoelectronic devices.