Bright and pure single-photon source in a silicon chip by nanoscale positioning of a color center in a microcavity

Abstract

We present an all-silicon source of near-infrared linearly-polarized single photons, fabricated by nanoscale positioning of a color center in a silicon-on-insulator microcavity. The color center consists of a single W center, created at a well-defined position by Si$^{+}$ ion implantation through a 150 nm-diameter nanohole in a mask. A circular Bragg grating cavity resonant with the W's zero-phonon line at 1217 nm is fabricated at the same location as the nanohole. By Purcell enhancement of zero-phonon emission, we obtain a photon count rate of $1.29 \pm 0.01$ Mcounts/s at saturation under above-gap continuous-wave excitation with a Debye-Waller factor of $98.6\pm1.4 \%$. A clean photon antibunching behavior is observed up to pump powers ensuring saturation of the W's emission ($g^{(2)}(0)=0.06\pm0.02$ at $P=9.2P_{sat}$), evidencing that the density of additional parasitic fluorescent defects is very low. We also demonstrate the triggered emission of single photons with $93\pm2 \%$ purity under weak pulsed laser excitation. At high pulsed laser power, we reveal a detrimental effect of repumping processes, that could be mitigated using selective pumping schemes in the future. These results represent a major step towards on-demand sources of indistinguishable near-infrared single photons within silicon photonics chips.

Figures (5)

• Figure 1: Integration of W centers in circular Bragg grating cavities, and expected cavity effects.a, Implantation of Si$^+$ ions in SOI through a PMMA layer patterned with nanoholes. b, Activation of the W centers by thermal annealing. The microscopic structure of the W center is shown in the inset. c, Fabrication of CBG cavities centered on the nominal coordinates of the nanoholes. The intensity of the electromagnetic field in the central disk is shown in the inset. d, Schematic sectional view of a CBG cavity containing a single W center, with the relevant dimensions. The red double-arrow indicates the orientation of the transition dipole. e, Normalized spontaneous emission rate $F$ and collection efficiency $\eta$ for a numerical aperture of 0.65, as a function of the algebric distance $\Delta r$ between the dipole and the center of the cavity in the coordinate system shown in d.
• Figure 2: Polarization analysis of cavities containing W centers.a, Polarization-selective PL map sets of four arrays of cavities. The maps are recorded at a temperature of 10 K under above-gap CW excitation with a power of 13 $\mu$W. b, Polarisation diagram of the spot labeled as 'W-1'.
• Figure 3: Observation of a single W center in a CBG cavity.a, PL map of a single W center in a CBG cavity at saturation under CW excitation. b, PL saturation curve for the W in the CBG cavity under above-gap CW excitation. The PL intensity is integrated over the 1200 - 1300 nm spectral range. The black line is a fit to the saturation function for a two-level system, $I=I_{sat} / ( 1 + P_{sat}/P)$, with $I_{sat}=1.29 \pm 0.01$ Mcps and $P_{sat}=49 \pm 1$$\mu$W. c, Uncorrected second-order photon correlation histogram of the PL emission for $P = 135$$\mu$W = 2.8 $P_{sat}$. d, A zoom at short time delays reveals a $g^{(2)}(0)$ value of $0.03 \pm 0.01$
• Figure 4: Optical properties of a CBG-coupled W center.a, PL spectrum in the 1150 - 1450 nm spectral range. b, High-resolution PL spectrum and white-light reflectometry measurement of the cavity. The dashed grey line is a fit to a Lorentzian profile. c, PL decay of the emitter under triggered excitation with a repetition rate of 5 MHz and 17.5 $\mu$W average power.
• Figure 5: Triggered single photons from a CBG-coupled W center.a, Second-order correlation histogram $C(\tau)$ for $P$ = 0.5, 4.4 and 17.5 $\mu$W. The normalized area of each peak is given by the coordinate of the filled squares on the right axis. The dashed lines represent a fit of the peaks area to Equation \ref{['eqn:photoblinking']}. b, Zoom on the central peak. The numbers indicate the area of the peak for each power value. c, Zoom on the central peak for $P$ = 17.5 $\mu$W with 20 ps time-bins.