On the hunt for a near-infrared single photon emitter in silicon — Optical characterization of radiation damage defects in 28Si

Integrated silicon photonics allows for the routine control and detection of light down to the single photon regime with low loss and in a scalable way, but to date still has the reputation of lacking fast, efficient and indistinguishable optical emitters that can be easily coupled to photonic structures. The identification of such an emitter will further enable the realization of on-chip low-energy, speed-of-light processing, and could open up exciting prospects for quantum computing and quantum communications. A multitude of radiation damage centres in silicon show bright emission in or near the attractive telecommunication band wavelength range at temperatures up to tens of Kelvin, which is compatible with the state-of-the-art superconducting nanowire single-photon detectors. These centres have been thoroughly studied in natural silicon using a wide variety of techniques, but their detailed spectral properties remained hidden by inhomogeneous line broadening due to the mixed isotopes present in natural silicon. We characterize three defect centres showing potential as single photon emitters, the C centre (790 meV, or 1571 nm), the G centre (969 meV, or 1280 nm), and the W centre (1019 meV, or 1217 nm). Performing ultra-high-resolution spectroscopy on ensembles of these defects in highly isotopically enriched 28Si, where isotopic inhomogeneous line broadening is removed, reveals a dramatic reduction in spectral linewidth of up to two orders of magnitude. We also report for the first time a quartet structure of the G centre that is revealed in 28Si, and a G linewidth that is only twice the lower bound given by the excited state lifetime. These results have direct implications for the spectral widths and fine structure to be expected from individual emitters, even in natural silicon.