Optical control of the exciton charge states of single quantum dots via impurity levels

The impact of residual impurities on neutral and charged exciton complexes in single InGaAs quantum dots (QDs) grown by metalorganic chemical vapor deposition were investigated by microphotoluminescence combined with photon correlation measurements. We show that the formation of a charged exciton can be controlled by using resonant excitation to the residual impurity level. This optical excitation scheme is useful for the selective generation of only charged excitons in initially neutral QDs without sophisticated sample designs.

Figure 1

(a) The $\mu \mathrm{PL}$ spectrum of the unmasked regions. (b) The power evolution of single QD spectra for $E_{\mathrm{ex}}=1520\mathrm{meV}$. (c) The intensities of $X$, $2X$, and $X^{-}$ lines as a function of the excitation power.

Figure 2

Autocorrelation of $X$ line (a) and cross-correlations obtained by using $2X$ and $X$ lines (b), $X$ and $X^{-}$ lines, (c) as well as $2X$ and $X^{-}$ lines, and (d) as start and stop triggers.

Figure 3

(Color online) (a) Single QD spectra under different $E_{\mathrm{ex}}$’s. (b) and (c) The optical processes for above-band excitation and resonant excitation to the carbon acceptor level.

Figure 4

(a) The power evolution of a single QD spectra for $E_{\mathrm{ex}}=1494\mathrm{meV}$. (b) The intensities of $X$, $2X$ and $X^{-}$ as a function of excitation power. (c),(d) The energies of the $X^{-}$ and $X$ lines as a function of excitation power. $P_{\mathrm{sat}}$ of the $X^{-}$ line is indicated by a vertical dotted line. The inset in (d) shows the $X$ peak doublet at $P_{\mathrm{sat}}$.