Effect of soft annealing on optoelectronic performances of Ti-hyperdoped Si photodiodes

We investigate the impact of soft furnace annealing (250–450 °C) on the optoelectronic performance of Ti-hyperdoped Si photodiodes. The annealing step, introduced between Ti ion implantation and nanosecond pulsed laser melting (ns-PLM), was designed to improve the crystalline quality of the seed layer from which ns-PLM recrystallizes the implanted region. For Ti doses of 1 × 1015 and 2 × 1015 cm−2, soft annealing enhanced the minority carrier lifetime and reduced the diffusion saturation current, leading to improved external quantum efficiency (EQE) above the Si absorption edge (photon energies higher than 1.12 eV). At higher implantation doses, however, these improvements were less pronounced, suggesting a dose-dependent interplay between defect passivation and recrystallization dynamics. However, EQE in the sub-bandgap range slightly decreased after annealing for both dose levels, while high-dose samples consistently exhibited stronger photoresponse, indicating that process-induced defects may contribute beneficially to sub-bandgap absorption in Ti-hyperdoped Si. These findings highlight soft annealing as a practical means of tailoring carrier dynamics and optical response in Ti-hyperdoped Si. By balancing defect passivation and controlled defect retention, this approach opens new opportunities for optimizing Ti-hyperdoped Si photodiodes toward applications in broadband light detection, short-wave infrared sensing, and CMOS-compatible optoelectronics.