Surface passivation for narrowing optical linewidth of silicon T centers in nanophotonic devices
AuthorsFariba Islam, Chang-Min Lee, Kyu-Young Kim, Sorah Fischer, Purbita Purkayastha, Edo Waks
Resources
A thin Al2O3 coating makes silicon T-center photons more spectrally stable, bringing indistinguishable telecom quantum emitters closer to practical devices.
Key results
Largest reduction in the optical linewidth of a passivated silicon T center
Average same-emitter improvement across four T centers
Optimal passivation thickness in nanometers
Approximately 75 MHz inferred from spectral-hole burning
What the paper found
This study demonstrates atomic-layer-deposited Al₂O₃ surface passivation as a CMOS-compatible method for reducing spectral diffusion in silicon T centers integrated into nanophotonic devices. Photoluminescence-excitation measurements on the same emitters showed an average optical-linewidth reduction of 32%, with a maximum reduction of 57%; one transition narrowed from 2.41 GHz to 1.04 GHz. Thickness sweeps identified 11 nm of Al₂O₃ as optimal: thicker films provided little additional narrowing and instead increased strain-related non-radiative decay. Continuous 980 nm above-bandgap illumination further reduced a passivated emitter’s linewidth to approximately 0.3–0.4 GHz, indicating that nearby charge traps remain active after surface treatment. Spectral-hole burning measured a 150.8 ± 22.0 MHz hole, placing an upper bound of approximately 75 MHz on the homogeneous linewidth and showing that slow spectral diffusion remains the dominant broadening mechanism. The results establish surface passivation, potentially combined with atomic-layer etching, electrical charge stabilization, and cavity integration, as a route toward more indistinguishable telecom-band photons from silicon T centers.
Original abstract
Silicon T centers are promising spin-photon interfaces in solid-state platforms for telecom-compatible, scalable quantum information technologies. A major challenge for T centers in nanophotonics is spectral diffusion, where fluctuations in the local electric-field environment from surface and bulk charge states broaden the optical transition and reduce photon indistinguishability. Strategies that directly suppress spectral diffusion are therefore critical for improving T-center-based quantum photonic devices. Here, we use atomic-layer-deposited Al2O3 to passivate the silicon surface and demonstrate a systematic narrowing of T center optical linewidths. Across our measurements, Al2O3 passivation reduces the T center emission linewidth by up to 57%. Complementary above-bandgap illumination and spectral hole burning measurements show that the remaining linewidth contains a significant spectral-diffusion component caused by adjacent charge traps, while placing an upper bound of approximately 75 MHz on the homogeneous linewidth. This work provides a CMOS-compatible path toward generating indistinguishable photons from silicon T centers for scalable quantum photonic applications.
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