A.A. Khandekar

Microstructure of lateral epitaxial overgrown InAs on (100) GaAs substrates

Substantial defect reduction was achieved in InAs/GaAs by lateral epitaxial overgrowth in which InAs was grown on mask-patterned (100) GaAs with stripe-shaped windows of various widths by metalorganic chemical vapor deposition. The InAs growth morphology, crystal quality, and microstructure were evaluated using double-crystal x-ray rocking curves and scanning and transmission electron microscopy. The microstructure of the InAs grown on mask-free control samples was comprised of micron-scale misoriented grains and dislocations at a density of 1011 cm−2. As the width of the mask openings decreased to 0.8 μm, the rocking curves narrowed, grain boundaries disappeared and the dislocation density decreased to <107 cm−2. The distribution of the remaining defects suggests substantial changes in microstructural development when the window width is ≲1 μm.

Long wavelength emission of InGaAsN∕GaAsSb type II “W” quantum wells

Low temperature (30K) long wavelength photoluminescence emission (λ=1400–1600nm) from metalorganic chemical vapor deposition grown InGaAsN–GaAsSb type II “W” quantum wells (QWs), on GaAs substrates has been demonstrated. Thin layers (2–3nm) and high antimony-content (30%) GaAsSb were utilized in this study for realizing satisfactory wave function overlap and long wavelength emission. Tensile strained GaAsP barriers effectively improve the material structural and luminescence properties of the compressive strained active region. Room temperature photoluminescence data show that the type-II QW design is a promising candidate for realizing long wavelength GaAs-based diode lasers beyond 1500nm.

Characteristics of GaAsN∕GaAsSb type-II quantum wells grown by metalorganic vapor phase epitaxy on GaAs substrates

Pseudomorphic four-period GaAs0.978N0.022∕GaAs0.78Sb0.22 type-II multiquantum well structures were grown on (100) GaAs substrates by metalorganic vapor phase epitaxy at 530°C. The GaAs0.978N0.022 layers were grown at a V/III ratio of 685 and N∕V ratio of 0.96, whereas the GaAs0.78Sb0.22 was grown at a V/III ratio of 3.8 and Sb∕V ratio of 0.8. The superlattice peaks in the x-ray diffraction θ-2θ scans around the (400) GaAs peak were fitted using a dynamical simulation model to determine layer thickness and alloy compositions. The GaAsN and GaAsSb thicknesses were ∼8nm and ∼5nm, respectively. The photoluminescence (PL) spectra were obtained at 30K and the PL peak energy was found to match the type-II transition energy obtained from a 10-band k∙p model. Postgrowth annealing under arsine-H2 with a N2 cooldown was found to increase the low temperature PL intensity and result in the appearance of luminescence at room temperature.

Towards intersubband quantum box lasers: Electron-beam lithography update

We report on the progress in the patterning and fabrication of the intersubband quantum-box (QB) laser structure. From a patterning point of view our goal is to make 30-nm-diameter SiO2 and/or hydrogen silsesquioxane (HSQ) disks on 60–80nm centers on a GaAs surface to serve as masks for in situ etch and regrowth of QBs. Electron-beam lithography with high-resolution negative resist HSQ was used, and two processes have been investigated. The first process is to pattern HSQ directly on the GaAs surface, while the second one involves putting down an intermediate oxide layer first, followed by the e-beam lithography and the transfer of the pattern into the oxide. Problems were encountered with the e-beam patterning of HSQ directly on the GaAs surface because of the broad scattering from the substrate and not very good adhesion. Excellent patterning was demonstrated when the intermediate oxide layer was present between the GaAs substrate and the HSQ resist.

Formation of regular arrays of submicron GaAs dots on silicon

A combination of photolithography written with a near-field scanning optical microscope, gallium electrodeposition, and arsine annealing was used to produce regular arrays of submicron GaAs dots on a silicon substrate. Electrodeposition on a patterned Si surface produced an array of roughly hemispherical Ga dots. Annealing in arsine converted the gallium to GaAs, and caused the dots to develop faceted features. Transmission electron microscope measurements showed that the GaAs dots were polycrystalline, but had only a few grains. The dots did not have a preferred orientation relative to the substrate. Metalorganic chemical vapor deposition growth occurred selectively on these dots, forming regular arrays of GaAs disks up to 20μm in diameter. The GaAs disks exhibited characteristic GaAs low-temperature photoluminescence. This method has application for precisely positioning semiconductor dots or tailoring the grain size of polycrystalline films.

High antimony content GaAs1−zNz–GaAs1−ySby type-II “W” structure for long wavelength emission

GaAs1−zNz–GaAs1−ySby type-II “W” structures were studied for long wavelength (1300–1600 nm) applications. These structures were grown on a GaAs substrate using metal-organic vapor phase epitaxy. The antimony and nitrogen compositions in the pseudomorphic GaAs1−ySby and GaAs1−zNz were estimated by separately growing GaAs1−ySby–GaAs and GaAs1−zNz–GaAs strained superlattices. X-ray studies indicate that a maximum of y=0.37 antimony can be incorporated in the pseudomorphic GaAs1−ySby film grown using triethyl gallium (TEGa), trimethyl antimony (TMSb) and arsine (AsH3) at the growth temperatures employed. A postgrowth anneal was used to improve the emission intensity but leads to shifts in the emission wavelength. An emission wavelength as long as 1.47 μm was realized using a GaAs1−zNz–GaAs1−ySby–GaAs1−zNz structure.

Lateral Epitaxial Overgrowth of InAs on (100) GaAs Substrates

The microstructure of epitaxial InAs thin films grown by MOCVD on mask-patterned “LEO” (lateral epitaxial overgrowth) GaAs and on unpatterned GaAs substrates was studied using double-crystal x-ray diffraction, scanning electron microscopy and cross-sectional transmission electron microscopy. This paper describes the improvement in crystal quality (factor of 20 reduction in x-ray rocking curve width), the order of magnitude reduction in dislocation density, and the rearrangement of the remaining extended defects that were observed in the LEO material when compared to the film grown on the unpatterned wafer.

GaAsSb-GaAsN -based type-II ‘W’ structures for mid-IR emission

GaAsSb-GaAsN-based type-II ‘W’ structures have been studied for mid-IR (1.3–1.6µm) emission. Post growth annealing increases the photoluminescence (PL) intensity of the structures. Temperature dependent PL show a charge localization effect due to presence of nitrogen.

InGaAsN/GaAsSb/GaAs(P) Type-II ‘W’ quantum well lasers

InGaAsN/GaAsSb dasiaWpsila type-II strain compensated quantum well lasers on GaAs substrates are grown by MOCVD. Preliminary lasers with 3-stage active regions exhibit emission that is blue-shifted from the PL, due to charge separation and higher-energy transitions.