Excitonic molecule in a quantum dot: Photoluminescence lifetime of a single $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot

Time dependence of the photoluminescence (PL) attributed to the exciton and biexciton in a single $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot is investigated at $4.3\mathrm{K}$ with microscopic spectroscopy. Dynamical behavior of the PL decay and the excitation intensity dependence of the exciton and biexciton PL are analyzed by rate equations assuming a cascading recombination from the biexciton to exciton state. The analysis shows that the biexciton lifetime is longer than the exciton lifetime. The estimated ratio of the biexciton lifetime to the exciton lifetime shows a molecular nature of the biexciton in the large quantum dots compared with the exciton Bohr radius.

Figure 1

(a) PL spectra of a single quantum dot observed through $0.6\text{−}\mu \mathrm{m}$-diameter metal mask aperture at different excitation intensities. Peak labeled with $X$ is attributed to the exciton recombination, peak labeled $B$ to the biexciton recombination. (b) Integrated intensities of peak $X$ (open square) and $B$ (filled square) as a function of the excitation power intensity. Dashed line is linear to the excitation intensity.

Figure 2

Time-resolved luminescence intensities of PL peak $B$ (filled circles) and $X$ (open circles) at the excitation intensity of $60\mathrm{nW}$ [column (a)], and $30\mathrm{nW}$ [column (b)]. Solid curves represent the numerical solutions of the coupled rate equations explained in the manuscript.

Figure 3

Ratio of the integrated PL intensity of biexciton to that of exciton as a function of the initial ratio of the population probability $p_{B0}∕p_{X0}$. Solid and dotted curves correspond to the cases where ${\tau }_X∕{\tau }_B=0.33$ and 2, respectively. Filled circles represent $I_B∕I_X$ estimated according to Fig. 2a (indicated by $a$) and 2(b) (indicated by $b$).