Investigation of the nonresonant dot-cavity coupling in two-dimensional photonic crystal nanocavities

We study the optical emission from single semiconductor quantum dots coupled to the optical modes of photonic crystal nanocavities. For dots that are both spectrally and spatially coupled, autocorrelation measurements reveal efficient single photon generation, with a drastically reduced lifetime due to the Purcell effect. However, the multiphoton emission probability is enhanced compared to the same quantum dot (QD) transition when it is detuned from the cavity mode by controlled ${\mathrm{N}}_2$ deposition. This indicates the presence of an emission background that is shown to be related to the dot by using photon cross-correlation spectroscopy. Photon temporal correlations persist even for large spectral detunings beyond $\Delta \lambda \sim -10\mathrm{nm}$, excluding the intrinsic QD continuum and phonon mediated processes as being responsible for the cavity mode emission background. We propose a mechanism based on photon induced shake up processes in the charged quantum dots, enhanced by the optical cavity.

Figure 1

(Color online) (a) $\mu \text{−}\mathrm{PL}$ spectra recorded from a single QD coupled to a cavity mode for weak (red/gray) and strong (gray) cw pumping. The gray shaded region indicates the mode background emission. (Inset) Scanning electron micrograph of the $L3$ cavity investigated. (b) $\mu \text{−}\mathrm{PL}$ spectra of the same QD and the spectrally shifted cavity mode after ${\mathrm{N}}_2$ deposition. (c) PL intensity as a function of the excitation power for the $X_a$ and $X_b$ lines.

Figure 2

(Color online) (Left panels) Autocorrelation measurements and corresponding time-resolved data (right panels) for (a) $X_a$ and (b) $X_b$. The two panels in (b) compare the data for $X_b$ coupled to the cavity mode before ${\mathrm{N}}_2$ deposition with the case when $X_b$ is spectrally detuned from the cavity mode after ${\mathrm{N}}_2$ deposition. An autocorrelation of the mode background is shown in gray.

Figure 3

(Color online) Cross-correlation measurements between (a) $X_a$ and $X_b$, (b) between $X_a$ and cavity mode before ${\mathrm{N}}_2$ deposition, and (c) between $X_a$ and cavity mode after ${\mathrm{N}}_2$ deposition. We show the original data in gray and the corresponding smoothed data in red/gray.

Figure 4

(Color online) Energy diagram with initial state $\mid i⟩$ and two final state configurations $\mid f^{\mathit{con}}⟩$ and $\mid f^{\mathit{dis}}⟩$ and the corresponding QD occupations for a heavily positively charged dot.