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

Baptiste Lefaucher, Yoann Baron+9 more|ArXiv.org|Jan 22, 2025

Advanced Fluorescence Microscopy Techniques3 citations

TL;DR

This paper demonstrates an all-silicon, on-chip single-photon source by deterministically placing a W center in a circular Bragg grating cavity on SOI, achieving high Purcell-enhanced ZPL emission with excellent single-photon purity under CW and pulsed excitation.

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.

Motivation & Objective

• Demonstrate deterministic on-chip generation of bright, pure single photons in silicon using nanoscale emitter positioning.
• Achieve strong Purcell enhancement of zero-phonon line emission for W centers in circular Bragg grating cavities.
• Assess the single-photon purity, brightness, and polarization properties under CW and pulsed excitation.
• Evaluate the potential and limitations for scalable, indistinguishable on-chip photon sources in silicon photonics.

Proposed method

• Fabricate an array of W centers by Si+ ion implantation through 150 nm nanoholes in a PMMA mask on SOI.
• Create circular Bragg grating (CBG) cavities centered at the nanohole locations and resonant with the W ZPL at 1217–1218 nm.
• Characterize emission by photoluminescence spectroscopy and second-order correlation g(2)(τ) under above-gap CW and pulsed excitation.
• Analyze cavity-emitter coupling via reflectometry to extract the cavity Q factor and Purcell enhancement.
• Estimate zero-phonon line fraction and Purcell-enhanced radiative decay through lifetime measurements under pulsed pumping.

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.

Experimental results

Research questions

• RQ1 Can a single W center be deterministically positioned at a cavity antinode to maximize Purcell enhancement in an on-chip silicon photonic structure?
• RQ2 What are the resulting brightness, purity (g(2)(0)), and ZPL fraction achievable for a W-center in a SOI CBG cavity under CW and pulsed excitation?
• RQ3 How does the emitter-cavity detuning and positioning tolerance affect collection efficiency and Purcell factor in this system?
• RQ4 What are the main limitations (blinking, non-radiative channels) and prospects for improving on-chip indistinguishable single-photon emission from silicon color centers?

Key findings

• A W center is deterministically created at a location aligned with the cavity antinode, achieving strong Purcell-enhancement of ZPL emission.
• Observed CW saturation count rate around 1.29 Mcps with g(2)(0) ≈ 0.03–0.06 over the full power range, indicating very low parasitic emission.
• Zero-phonon emission fraction is ~98.6% of the PL, indicating efficient ZPL emission due to cavity Purcell enhancement.
• A polarized, linearly-polarized single-photon source with high purity is demonstrated under weak pulsed pumping, achieving 93% purity for triggered emission.
• Cavity reflectometry yields a mode with Q ≈ 158 (Δλ ≈ 7.7 nm), closely matching simulations and indicating effective spectral alignment of ZPL with the cavity mode.
• Triggered emission under pulsed excitation shows antibunching with a central peak area corresponding to single-photon emission, while blinking (metastable-state dynamics) is observed and analyzed.
• Demonstrated a significant enhancement over unpatterned SOI W centers (enhancement factor ~400 in PL count rate at saturation), highlighting the cavity’s role in brightness.

Figure 2: 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 b