Room-temperature 1.54 µm photoluminescence of Er:O_x centers at extremely low concentration in silicon

The demand for single photon sources at λ = 1.54 µm, which follows from the consistent development of quantum networks based on commercial optical fibers, makes Er:O_x centers in Si still a viable resource thanks to the optical transition of Er³⁺: ⁴I₁₃/₂ → ⁴I₁₅/2. Yet, to date, the implementation of such system remains hindered by its extremely low emission rate. In this Letter, we explore the room-temperature photoluminescence (PL) at the telecomm wavelength of very low implantation doses of Er:O_x in Si. The emitted photons, excited by a λ = 792 nm laser in both large areas and confined dots of diameter down to 5 µm, are collected by an inverted confocal microscope. The lower-bound number of detectable emission centers within our diffraction-limited illumination spot is estimated to be down to about 10⁴, corresponding to an emission rate per individual ion of about 4 ×10³ photons/s.