Probing the Spontaneous Emission Dynamics in Si-Nanocrystals-Based Microdisk Resonators

As a possible cavity quantum electrodynamical system, unlike III–V quantum dots, Si-NCs are not considered ideal emitters for emission rate enhancement observations (Purcell effect). Here, we report on direct measurements of spontaneous emission rate enhancement of Si-NCs embedded in a whispering-gallery mode resonator at room temperature. Using time-resolved microphotoluminescence experiments, we demonstrate important lifetime reductions ($\sim 70\%$) for Si-NCs coupled to cavity modes with respect to uncoupled ones. Comparing experiments with the theoretical Purcell enhancement in a bad emitter regime, we estimate effective linewidths of $\sim 10\mathrm{meV}$ through which Si-NC emitters are coupled to cavity photons. Finally, our study provides an alternative method for the estimation of subnatural linewidths of quantum dots at room temperature.

Figure 1

(a) Cross-sectional scanning electron microscopy images of microdisk resonators. (b) PL intensity of quasi-TM WGMs with the calculated quality factors (●, ▾). (c) Numerically calculated mode volumes. (d) The calculated cavity figure-of-merit—ideal Purcell factor $F_P$.

Figure 2

(a) Graphical sketch explaining the use of exponential decay functions for on- and off-resonance conditions. (b) The fitting parameter $A$ in Eq. (1) has been defined as the PL intensity ratio of the mode $I_{\mathrm{mode}}$ and the background $I_{\mathrm{base}}$. (c) The extracted values of parameter $A$ from the PL spectra of Fig. 1b.

Figure 3

Measured out-of-resonance (full squares, $\lambda =853\mathrm{nm}$) and on-resonance (empty circles, $\lambda =846\mathrm{nm}$) PL signals. The data have been fitted using single and double stretched exponentials, respectively. The inset shows the associated KWW lifetime distributions.

Figure 4

(a) Measured PL lifetimes for the peaks (●, ▾) and dips (○, ▽) of the WGM spectrum. (b) Calculated lifetime shortening $ϵ=\frac{{\tau }_{\mathrm{dip}}}{{\tau }_{\mathrm{peak}}}$ and (c) the estimated Si-NC effective linewidth at room temperature.