Abstract:
An electron-microscopy study of GaAs structures, grown by molecular-beam epitaxy, containing two coupled layers of InAs semiconductor quantum dots (QDs) overgrown with a thin buffer GaAs layer and a layer of low-temperature-grown gallium arsenide has been performed. In subsequent annealing, an array of As nanoinclusions (metallic QDs) was formed in the low-temperature-grown GaAs layer. The variation in the microstructure of the samples during temperature and annealing conditions was examined. It was found that, at comparatively low annealing temperatures (400–500$^\circ$C), the formation of the As metallic QDs array weakly depends on whether InAs semiconductor QDs are present in the preceding layers or not. In this case, the As metallic QDs have a characteristic size of about 2–3 nm upon annealing at 400$^\circ$C and 4–5 nm upon annealing at 500$^\circ$C for 15 min. Annealing at 600$^\circ$C for 15 min in the growth setup leads to a coarsening of the As metallic QDs to 8–9 nm and to the formation of groups of such QDs in the area of the low-temperature-grown GaAs which is directly adjacent to the buffer layer separating the InAs semiconductor QDs. A more prolonged annealing at an elevated temperature (760$^\circ$C) in an atmosphere of hydrogen causes a further increase in the As metallic QDs’ size to 20–25 nm and their spatial displacement into the region between the coupled InAs semiconductor QDs.
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