Correlated photon-pair emission from a charged single quantum dot

The optical creation and recombination of charged biexciton and trion complexes in an $(\mathrm{In},\mathrm{Ga})\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot is investigated by microphotoluminescence spectroscopy. Under the condition of quasiresonant pulsed excitation into the $p$ shell we find nearly background-free photoluminescence from single quantum dots where multiple-photon $(>1)$ emission is fully suppressed. This reflects almost perfect triggered single-photon emission. Photon cross-correlation measurements demonstrate the temporally correlated decay of charged biexciton and trion states. Our calculations provide strong evidence for radiative decay from the excited trion state, thus indicating a long-lived $p$-electron spin configuration.

Figure 1

(Color online) (a) $\mu$-PL spectra from a single (In,Ga)As QD as observed for off-resonant (i.e., above-barrier) cw laser excitation. (b) Spectra taken on the same QD under quasiresonant ($p$-shell) excitation revealing PL lines being addressed to charged complexes. Horizontal markers: filter bandpass for photon correlation experiments. (c),(d) cw power dependence of neutral and charged QD states under off-resonant (c) and quasiresonant (d) excitation.

Figure 2

(Color online) (a) Photon autocorrelation measurement under ps pulsed quasiresonant excitation $(E_{\mathit{exc}}=1.407\mathrm{eV})$ as obtained from the $1.340\text{‐}\mathrm{eV}$ PL line [see Fig. 1b]. Numbers: Poisson-normalized peak areas. (b) Cross-correlation trace obtained from the $1.3400\text{‐}\mathrm{eV}$ (${\mathrm{XX}}^{-}$: “start”) and $1.3362\text{‐}\mathrm{eV}$ (${\mathrm{X}}^{-*}$: “stop”) PL lines in Fig. 1b.

Figure 3

(a) Scheme of the ${\mathrm{XX}}^{-}\to {\mathrm{X}}^{-*}\to e$ cascade: Starting from the charged biexciton ground state $A$, an excited charged exciton state $B$ is reached by a e-h recombination process. The subsequent recombination step leads to an excited dot state $C$ with only one electron. (b) Trion configurations with opposite spins for the $s$ and $p$ electrons.