Self-Organized Superlattices in GaInAsSb Grown on Vicinal Substrates

Self-organized superlattices are observed in GaInAsSb epilayers grown lattice matched to vicinal GaSb substrates. The natural superlattice (NSL) is oriented at a slight angle of about 4{sup o} with respect to the vicinal (001) GaSb substrate. This vertical composition modulation is detected at the onset of growth. Layers in the NSL are continuous over the lateral extent of the substrate. Furthermore, the NSL persists throughout several microns of deposition. The NSLs have a period ranging from 10 to 30 nm, which is dependent on deposition temperature and GaInAsSb alloy composition. While the principle driving force for this type of phase separation is chemical, the mechanism for the self-organized microstructure is related to local strains associated with surface undulations. By using a substrate with surface undulations, the tilted NSL can be induced in layers with alloy compositions that normally do not exhibit this self-organized microstructure under typical growth conditions. These results underscore the complex interactions between compositional and morphological perturbations

Effect of Substrate Orientation on Phase Separation in Epitaxial GaInAsSb

The effect of substrate misorientation on phase separation in Ga{sub 1-x}In{sub x}As{sub y}Sb{sub 1-y} nominally lattice-matched to GaSb is reported. The layers were grown at 575 C by organometallic vapor phase epitaxy on vicinal (001) GaSb substrates, miscut 2{sup o} {yields} (-111)A, (1-11)B, or (101). Ga{sub 1-x}In{sub x}As{sub y}Sb{sub 1-y} (x {approx} 0.1, y {approx} 0.09) layers, which have 300-K photoluminescence (PL) peak emission at {approx}2.1 {micro}m, grow step-bunched and exhibit minimal phase separation. The full width at half maximum of 4-K PL spectra is slightly smaller at 7 meV for layers grown on substrates miscut toward (1-11)B compared to 9 meV for layers grown on substrates miscut toward (-1-11)A and (101). Ga{sub 1-x}In{sub x}As{sub y}Sb{sub 1-y} layers with higher alloy composition (0.16 {le} x {le} 0.19, 0.14 {ge} y {le} 0.17), which have 300-K PL peak emission at {approx}2.4 {micro}m, have significant phase separation. These layers are characterized by increased lattice constant variations and epitaxial tilt, broad PL spectra with significant band tailing, and strong contrast modulation in transmission electron microscopy. The degree of decomposition depends on substrate miscut direction: Ga{sub 1-x}In{sub x}As{sub y}Sb{sub 1-y} layers grown on (001) 2{sup o} {yields} (1-11)B substrates are more homogeneous than those grown on (001) 2{sup o} {yields} (-1-11)A and (001) 2{sup o} {yields} (101) substrates. The results are attributed to the smaller adatom diffusion length on substrates miscut toward (1-11)B

Phase-controlled, heterodyne laser-induced transient grating measurements of thermal transport properties in opaque material

The methodology for a heterodyned laser-induced transient thermal grating technique for non-contact, non-destructive measurements of thermal transport in opaque material is presented. Phase-controlled heterodyne detection allows us to isolate pure phase or amplitude transient grating signal contributions by varying the relative phase between reference and probe beams. The phase grating signal includes components associated with both transient reflectivity and surface displacement whereas the amplitude grating contribution is governed by transient reflectivity alone. By analyzing the latter with the two-dimensional thermal diffusion model, we extract the in-plane thermal diffusivity of the sample. Measurements on a 5 {\mu}m thick single crystal PbTe film yielded excellent agreement with the model over a range of grating periods from 1.6 to 2.8 {\mu}m. The measured thermal diffusivity of 1.3 \times 10-6 m2/s was found to be slightly lower than the bulk value.Comment: 19 pages, 6 figure

Evolution of Surface Structure and Phase Separation in GaInAsSb

Atomic force microscopy was used to study changes in the surface step structure of GaInAsSb layers with varying degrees of phase separation. The layers were grown by organometallic vapor phase epitaxy on (001) GaSb substrates with 2{sup o} miscut angles toward (-1-11)A, (1-11)B, and (101). Alloy decomposition was observed by contrast modulations in plan-view transmission electron microscopy, and broadening in x-ray diffraction and photoluminescence peaks. GaInAsSb layers with a minimal degree of phase separation exhibit a step-bunched step structure. A gradual degradation in the periodicity of the step structure is observed as the alloy decomposes into GaAs- and InSb-rich regions. The surface eventually develops trenches to accommodate the local strain associated with composition variations, which are on the order of a few percent. The surface composition is affected by substrate miscut angle, and although phase separation cannot be eliminated, its extent can be reduced by growing on substrates miscut toward (1-11)B

AlGaAsSb/GaSb Distributed Bragg Reflectors Grown by Organometallic Vapor Phase Epitaxy

The first AlGaAsSb/GaSb quarter-wave distributed Bragg reflectors grown by metallic vapor phase epitaxy are reported. The peak reflectance is 96% for a 10-period structure

Reduction of defect density by rapid thermal annealing in GaAsBi studied by time-resolved photoluminescence

International audienceTime-resolved photoluminescence was performed on as-grown and annealed bulk GaAsBi samples. Rapid thermal annealing was carried out at a temperature of 750 °C. With annealing, we observed a significant change in the photoluminescence decay time at low temperature and low excitation power, which is likely due to a reduction of localized states. Although the time-integrated photoluminescence intensity did not show a large variation, this enhancement was confirmed by the observed removal after annealing of the S-shape behaviour present in the as-grown sample