AFM images of the three samples in this study. Samples A, B, and C are shown in (a), (b), and (c), respectively. Image sizes are is 2.2 × 2.2 μm2 for (a) and 1 × 1 μm2 for (b) and (c).
Reflectivity data vs time delay. Data from samples A, B, and C (as indicated) for two different pump intensities (values are relative to maximum intensity) are shown in (a). Data for A and B are vertically shifted for clarity. For comparison, reflectivity from GaAs(100) is shown in the inset of (a). Fits to reflectivity data are illustrated in (b) and (c) for samples B and C at a relative laser intensity of 0.7 and 0.34, respectively.
Fast capture time vs laser intensity for samples A, B, and C. Symbols are results of fitting the reflectivity data. Solid lines are guides to the eye.
Results of 1D diffusion model. (a) Carrier density vs distance z from sample surface at 5 different time delays tD . The vertical line indicates location of QL. For this panel t = 0.1 and c = 0.77, which produces a fast decay similar to that of sample C at low excitation levels. (b) Near-surface (0–20 nm) carrier density vs time delay for c = 0.3 and t = 0.1, which gives decay similar to that of samples A and B at low excitation level. Points are results of model; solid line is bi-exponential fit with decay times of 0.28 and 1.6 ps. (c) Near-surface carrier density vs time delay for c = 0.77 and t = 0.1, as in (a). Solid-line fit has decay times of 0.14 and 1.1 ps.
Sample growth parameters. Long sample designations (030907-1, e.g.) are for cross referencing to PL measurements. 6 Short designations (A, e.g.) are for internal reference in this paper. Also indicated are PL peak position and line width for ground-state QD emission.
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