Figure 1

(a) Schematics of a quantum cascade process when a biexciton ($2\mathrm{X}$) decays first to an exciton ($1\mathrm{X}$) and then to a ground state ($\mathrm{G}$) for an NQD coupled to the rough silver surface (scanning electron microscopy image in the lower left corner). (b) Hanbury Brown and Twiss setup consists of a $50:50$ beam splitter (BS) and two avalanche photodiodes (APDs). (c) Second-order photon correlation function $g^{(2)}(t)$ measured under pulsed excitation without any spectral selection. The area of the central peak [$g^{(2)}(t=0)$] measures the probability of creating 2X and subsequent emission of two photons via the quantum cascade process and can be expressed as $g^{(2)}(0)\approx Q_{2\mathrm{X}}{Q}_{1\mathrm{X}}⟨N{⟩}^2$ in the $⟨N⟩\to 0$ limit. The area of the side peak [$g^{(2)}(t=T)$; $T$ is the separation between sequential laser pulses] reflects the probability of exciton generation and emission in two successive excitation cycles and can be expressed as $g^{(2)}(T)\approx (Q_{1\mathrm{X}}⟨N⟩{)}^2$. Consequently, the degree of photon bunching given by $R=g^{(2)}(0)/g^{(2)}(T)$ approaches $R_0\approx Q_{2\mathrm{X}}/Q_{1\mathrm{X}}$ when $⟨N⟩\to 0$.Reuse & Permissions

Figure 2

$g^{(2)}$ functions of single giant NQDs deposited (a) on a rough silver surface and (b) on a quartz substrate. Insets in (a) and (b) display PL decay of a corresponding giant NQD. (c) Histograms of normalized zero-delay-peak areas measured for 35 giant NQDs on the quartz (open circles) and 37 giant NQDs on the rough silver film (blue bar). (d) The plot of $R_0$ vs average PL lifetime (diamonds, giant NQDs on the silver film; circles, reference giant NQDs).Reuse & Permissions

Figure 3

(a), (b) $g^{(2)}$ functions of two giant NQDs on a rough silver film acquired at three different pump powers. (c) Pump power dependences of $R$ of three different giant NQDs coupled to a rough silver film and a reference NQD plotted as a function of $⟨N⟩$.Reuse & Permissions

Figure 4

(a) Calculations of $R_0$ vs $\gamma$ for various values of $\alpha$ and $\beta$ (indicated in the figure). $\alpha$ value of 7 is selected based on $\sim 8$ fold reduction of the giant NQD quantum yield reported in Fig. S3 [8]. (b) Simulations of $R$ vs $⟨N⟩$ for $\gamma =1$ and different values of $\alpha$ and $\beta$ [same as in (a) using the same line styles and colors]. Squares: calculated trace for a reference giant NQD. Schematic for rapid recombination via (c) trap states forming a mid‐gap band and (d) uncorrelated tunneling of electrons and holes into the metal (d).Reuse & Permissions