Proper In deposition amount for on-demand epitaxy of InAs/GaAs single quantum dots*

The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots (SQDs) to raise the growth repeatability. Here, through many growth tests on rotating substrates, we develop a proper In deposition amount (θ) for SQD growth, according to the measured critical θ for test QD nucleation (θ c). The proper ratio θ/θ c, with a large tolerance of the variation of the real substrate temperature (T sub), is 0.964−0.971 at the edge and > 0.989 but < 0.996 in the center of a 1/4-piece semi-insulating wafer, and around 0.9709 but < 0.9714 in the center of a 1/4-piece N+ wafer as shown in the evolution of QD size and density as θ/θ c varies. Bright SQDs with spectral lines at 905 nm–935 nm nucleate at the edge and correlate with individual 7 nm–8 nm-height QDs in atomic force microscopy, among dense 1 nm–5 nm-height small QDs with a strong spectral profile around 860 nm–880 nm. The higher T sub in the center forms diluter, taller and uniform QDs, and very dilute SQDs for a proper θ/θ c: only one 7-nm-height SQD in 25 μm2. On a 2-inch (1 inch = 2.54 cm) semi-insulating wafer, by using θ/θ c = 0.961, SQDs nucleate in a circle in 22% of the whole area. More SQDs will form in the broad high-T sub region in the center by using a proper θ/θ c.

Source:IOPscience

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Fabrication of two-color surface emitting device of a coupled vertical cavity structure with InAs quantum dots formed by wafer bonding

We fabricated a two-color surface emitting device of a coupled cavity structure, which is applicable to terahertz light source. GaAs/AlGaAs vertical multilayer cavity structures were grown on (001) and (113)B GaAs substrates and the coupled multilayer cavity structure was fabricated by wafer bonding them. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode lights. The bonding position was optimized for the equivalent intensity of two-color emission. We formed a current injection structure, and two-color emission was observed by current injection, although no lasing was observed.

Source:IOPscience

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Tuning the bandgap of InAs quantum dots by selective-area MOCVD

In-plane bandgap energy control of InAs quantum dots (QDs) grown on GaAs substrates is demonstrated using selective-area epitaxy. Transmission electron microscopy and cathodoluminescence are used for characterization of the selectively grown dots. A single-step growth of a thin InAs quantum well and InAs QDs emitting at 1010 and 1100 nm (at 77 K) on the same wafer is demonstrated. Non-uniform growth profile is reported for the selectively grown QDs in the mask openings. Surface migration of adatoms from higher order facets to (1 0 0) facets results in enhanced deposition rates closer to the edge of the openings and vapour phase diffusion of adatoms results in density variations across the openings over length scales greater than the surface migration length of the adatoms.

Source:IOPscience

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InAs on Insulator by Hydrogen Implantation and Exfoliation

InAs on insulator structures were successfully fabricated using wafer bonding and hydrogen implantation and exfoliation processes. Material was exfoliated from either a bulk InAs substrate or from a metamorphic InAs layer grown by MBE via a graded buffer layer on InP. The InAs from the bulk substrate exfoliates as a uniform planar layer with a large surface roughness, ~150 nm, which is similar to the estimated straggle. Under certain conditions, the InAs from the graded buffer layer, however, exfoliates non-uniformly, only transferring long wires of InAs that lie along a specific [110] direction. The size and spacing of these wires resemble the cross-hatch induced by the graded buffer layer growth indicating the exfoliation is influenced by dislocation strain fields. High resolution x-ray diffraction indicates that strain-free InAs is transferred in both cases, however, mosaic tilt is induced into the transferred layer by the hydrogen implantation step.

Source:IOPscience

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