The test-QD in-situ annealing method
could surmount the critical nucleation condition of InAs single quantum dots or 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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