Exciton radiative lifetime controlled by the lateral confinement energy in a single quantum dot

We report on time-resolved measurements on single GaAs quantum dots formed at the interface fluctuation of a $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ quantum well. We measure exciton radiative lifetimes as short as $100\mathrm{ps}$, demonstrating that monolayer fluctuation quantum dots have larger oscillator strength than any other $\mathit{III}\text{−}\mathit{V}$ or $\mathit{II}\text{−}\mathit{VI}$ semiconductor quantum dots. Studying various single quantum dots, we demonstrate that the oscillator strength of a quantum dot is controlled by its lateral confinement energy.

Figure 1

(Color) Streak camera images measured for three excitation powers: $P_0=7\mathrm{W}∕{\mathrm{cm}}^2$, $2P_0$, and $5P_0$. The horizontal scale corresponds to energy, the vertical scale to time. The top of each image: time integrated spectrum (logarithmic scale). Left (respectively, right) side of the images: spectrally integrated emission as a function of time for $X$ (black) and for $XX$ (gray), for $P_0$ (respectively, $5P_0$). The lines are a linear fit to the emission decay for long time delay.

Figure 2

Squares: spectrally and temporally integrated intensity of the $X$ line (black) and of the $XX$ line (gray) as a function of the excitation power. Full lines: calculated $X$ and $XX$ intensities.

Figure 3

(a),(b) PL (thin line) and PLE (thick line) spectra for two QDs. (c) Symbols: radiative decay time as a function of the exciton confinement energy inside the QD. (d) Symbols: oscillator strength as a function of the QD lateral radius. (c),(d) The line is a guide to the eyes.