Fluorescence optimization and ratiometric thermometry of near-infrared emission in erbium/oxygen-doped crystalline silicon

Crystalline Si (c-Si) implanted with rare-earth erbium (Er) might offer a solution to the development of silicon-based optical amplifiers and lasers at communication wavelengths for integrated silicon photonics. However, Er doped (often with oxygen) c-Si traditionally suffers from a strong thermal quenching effect in luminescence, resulting in extremely low luminous efficiency. We recently adopted a deep cooling process to treat Er/O co-doped c-Si samples. After the treatment, the thermal quenching effect is suppressed and the room-temperature photoluminescence (PL) is improved by two orders of magnitude. In this work, we report the PL optimization by tuning parameters including annealing temperature and time, deep cooling rate, O and Er concentration, and their ratio. It was found that the PL performance is maximized at O:Er concentration ratio of ∼2.5 and annealing temperature of 950 °C for 5 min followed by a cooling rate as fast as −500 °C s⁻¹. In addition, the Er/O emission has two spectrally-resolved peaks at 6472 cm⁻¹ and 6510 cm⁻¹ and their intensity ratio is independent of excitation power but a linear function of temperature. This unique property, likely originated from the physics of Er, Si, and O chemical composites formed in the deep cooling process, allows us to develop reliable cryogenic temperature sensors with an accuracy of ±1.0 K in the 4–200 K range.