Single-photon emission from pyramidal quantum dots: The impact of hole thermalization on photon emission statistics

We report an experimental study of the emission statistics of excitonic complexes from a single quantum dot and their temperature dependence. The single photon emission from the exciton ground state is shown to persist up to $80\mathrm{K}$. The deterioration of single photon statistics is attributed to new biexciton emissions, which emerge in the vicinity of the main single-exciton peak at rising temperatures. We identify these biexcitonic states as being formed by either one hole or two holes occupying excited states and analyze their specific polarization and power-dependent signature.

Figure 1

Second-order correlation function $g^{\left(2\right)}\left(\tau \right)$ of $X$ emission line at different temperatures. Solid lines: fits of the measured correlation curves including temporal response of the HBT. The fitted decay times corresponding to temperatures increasing from $10\text{to}90\mathrm{K}$ are 1.2, 1.1, 1.3, 2, 3.5, and $4\mathrm{ns}$.

Figure 2

$\mu \mathrm{PL}$ spectra of the same pyramidal QD performed under identical experimental conditions as the temporal correlation measurements of Fig. 1. Gray curves—decomposition of the measured spectra (black lines) into its components as marked on the figure. Spectra are offset for clarity. Inset: Values of the experimental background “A” as measured from correlation curves on Fig. 1 (open circles) and calculated from spectra (black squares).

Figure 3

Semilogarithmic plot of photoluminescence time decay of the $X$ line at the temperatures of 10 and $80\mathrm{K}$.

Figure 4

(a) $\mu \mathrm{PL}$ spectra of a QD taken in a cleaved edge geometry. Black line—measured in polarization perpendicular to the growth axis, gray line—parallel to it. Emissions from different excitonic complexes are marked on the figure. $2X$ labels the biexciton emission, $XX_n{}^{\prime }$ and $X{X}_n$ are the biexcitonic emissions associated with excited hole states. Inset: picture of the cleaved edge excitation geometry. Intensity dependences with excitation power of the lines lying energetically lower than $X$ (b) and higher than $X$ (c). The straight lines indicate either a linear or a quadratic dependence on these logarithmic plots of the PL intensity vs excitation power.

Figure 5

Schematic representation of the cascade emission of biexcitonic states associated with the configurations $\left(e_1\text{−}{e}_1\text{−}{h}_2\text{−}{h}_2\right)$ in (a) and $\left(e_1\text{−}{e}_1\text{−}{h}_1\text{−}{h}_2\right)$ in (b) and (c). In the second configuration, there are two radiative channels for each of the spin multiplets of the biexcitonic state.

Figure 6

$\mu \mathrm{PL}$ spectra of a QD measured in cleaved edge geometry at the temperatures of 10 (a) and $50\mathrm{K}$ (b).