Figure 4: Single-photon emission from an optimised device.

(a) Image of the photoluminescence from a single QD within the cavity, collected under 630 nm LED illumination. Scale bar represents 5 μm. (b) Far-field image of the photoluminescence from a QD in a circular grating cavity, along with line cuts from the two-dimensional Gaussian fit to the data along the x and y axes, shown as solid white lines. The upper right inset shows a two-dimensional image plot of the interpolated data, while the bottom curves plot the (uninterpolated) experimental data (symbols) and their Gaussian fits (solid lines). (c) Photon flux into the 0.4 numerical aperture collection objective (left y axis) and at the detector (right y axis), plotted as a function of 780 nm excitation power (in saturation units), for a QD in a circular grating (QD in BE, red symbols) and in unpatterned GaAs (QD in bulk, black symbols). (d) Examples of photoluminescence spectra collected under different excitation power (colour coded in panel (c)). (e) Photon collection coincidence events measured under pulsed 857 nm excitation, using a Hanbury–Brown and Twiss set-up. The disappearance of the central peak (zoomed-in plot in the inset) is the signature of pure single-photon emission. The uncertainty value is given by the standard deviation in the area of the peaks away from time zero. See Supplementary Fig. 2 for additional relevant data. (f) Time-resolved photoluminescence measurements collected under pulsed 780 nm excitation, showing the excited state decays (symbols) fitted by single exponential curves (solid lines). The shaded grey areas correspond to the 95% confidence intervals in the fit.