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

Source: iopscience

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