Ground and excited state energy trend in $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{Ga}\mathrm{As}$ quantum dots monitored by scanning photoluminescence spectroscopy

This paper presents a temperature-dependent scanning photoluminescence spectroscopic study of the ground and excited states on InAs quantum dots (QDs) inserted into ${\mathrm{In}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum wells. It is shown that structures exhibit a long-range spatial variation of the QD electronic states across the wafer. The observed trend of the ground state energy is attributed to the QD size variation and applied to explore multiple excited state energy shift versus ground state energy. Experimental results are compared with the electronic energy level dependence versus QD size predicted theoretically earlier on the basis of the eight-band $\mathbf{k}\bullet \mathbf{p}$ approximation.

Figure 1

PL spectra of the QD ensemble measured at different excitation power with the highest one of $1.0\mathrm{kW}∕{\mathrm{cm}}^2$.

Figure 2

Ground state PL band intensity dependence vs temperature. Excitation power density was $\sim 650\mathrm{W}∕{\mathrm{cm}}^2$.

Figure 3

(a) Map of PL intensity at $0.99\mathrm{eV}$ ($0.25\mathrm{mm}$ step size, $200\mu \mathrm{m}$ excitation spot diameter), (b) map PL intensity at GS max position, and (c) map of peak energy positions ($0.5\mathrm{mm}$ step size) at $\sim 90\mathrm{W}∕{\mathrm{cm}}^2$ power density. Arrow in (b) corresponds to spectroscopic line scans presented in Fig. 4.

Figure 4

PL spectra measured at 80 (a) and $300\mathrm{K}$ (b) at various PL intensity points on QD structure, see Fig. 3b. ($\sim 90\mathrm{W}∕{\mathrm{cm}}^2$ power intensity).

Figure 5

Ground state PL intensity vs GS maximum position measured at room temperature and $90\mathrm{W}∕{\mathrm{cm}}^2$ power intensity on four different QD structures grown at different temperatures: (1) $490°\mathrm{C}$, (2) $510°\mathrm{C}$, (3) $525°\mathrm{C}$, and (4) $535°\mathrm{C}$.

Figure 6

(a) Experimental peak positions for GS, first, and second ES vs GS peak energy measured at $80\mathrm{K}$ and excitation power intensity $650\mathrm{W}∕{\mathrm{cm}}^2$. (b) Theoretically calculated peak positions for GS, first, and second ES vs GS peak energy (or QD size) calculated on the basic of data in Ref. 10.