Temporal monitoring of nonresonant feeding of semiconductor nanocavity modes by quantum dot multiexciton transitions

We experimentally investigate the nonresonant $\left(\Delta E>5\text{meV}\right)$ feeding of photons into the optical mode of a two-dimensional photonic crystal nanocavity by quantum dot multiexciton transitions. Power-dependent photoluminescence measurements reveal a superlinear power dependence of the mode emission, indicating that the emission stems from multiexcitons. By monitoring the temporal evolution of the photoluminescence spectrum, we observe a clear anticorrelation of the mode and single exciton emission; the mode emission quenches as the population in the system reduces toward the single exciton level while the intensity of the mode emission tracks the multiexciton transitions. Our results lend strong support to a recently proposed mechanism [M. Winger et al., Phys. Rev. Lett. 103, 207403 (2009)] mediating the strongly nonresonant feeding of photons into the cavity mode.

Figure 1

(Color online) (a) Power-dependent PL spectra recorded from a QD-cavity system with two QDs, excitation level increasing from bottom to top. (b) Integrated PL intensity for the cavity mode (black stars), selected single exciton transitions from the $s$-shell of QD1 (labeled ${\text{X}}_1$—red circles) and from the $s$-shell of QD2 (labeled ${\text{X}}_2$—cyan rectangles). At higher power additional emission is observed from the $p$-shell multiexcitons of QD1 (blue triangles) and QD2 (green diamonds). (Inset) Scanning electron microscopy image of the photonic crystal L3 nanocavity.

Figure 2

(Color online) (a) Selected PL spectra of six different QD-cavity systems. [(b) and (c)] The exponents of the extracted cavity mode emission intensity obtained from power-dependent PL measurements of different QD-cavity systems plotted against the detuning relative to the (b) $s$-shell and (c) $p$-shell.

Figure 3

(Color online) (a) False color contour plot of the time-resolved PL intensity of a QD-cavity system as a function of emission wavelength (Ref. 21). (b) PL spectra at different time delays after the laser pulse, each integrated over 1 ns. [(c) and (d)] Extracted, normalized PL intensity for (c) ${\text{X}}_1$ (red circles) and ${\text{X}}_2$ (cyan rectangles), and (d) cavity mode (black stars), $p$-shell 1 (blue triangles), and $p$-shell 1 background (dark red diamonds) as a function of time delay after the laser pulse. The IRF is plotted as gray solid line. [(e)–(h)] Time-resolved PL intensity (logarithmic scale) for increasing excitation power (from bottom to top) for (e) the single exciton, (f) the biexciton of QD1, (g) a $p$-shell state, and (h) the cavity mode.