Improving charge carrier lifetime and mobility in hyperdoped silicon by seed quality engineering

The performance of hyperdoped silicon-based solar cells and photodetectors synthesized via ion implantation and pulsed laser melting can be enhanced by improving the fabrication process. Considering silicon self-implant as a model system, we show that there are two ways to reduce ion implantation defects and improve material quality: (1) increasing the pulsed laser melting depth and (2) introducing a pre-annealing step. This leads to improved charge carrier lifetimes and mobilities. We apply the pre-annealing method to tellurium- and gold-hyperdoped silicon samples and test the charge-carrier dynamics at two excitation wavelengths. After pre-annealing, for silicon self-implanted samples and tellurium-hyperdoped silicon samples, the carrier lifetime improves beyond our experimental detection limit (>4 ns) and a limited lifetime improvement is observed in gold-hyperdoped silicon. The improvement of mobility in silicon self-implanted sample is 1.3 times higher, two times higher in tellurium-hyperdoped silicon, and 1.1 times higher in gold-hyperdoped silicon after 350 °C pre-annealing. The improvement in carrier lifetime and mobility in Si:Te follows our model system, but the limited improvement in Si:Au suggests that dopant–defect interactions might limit the benefits of pre-annealing. Our study also shows that incorporating one additional step in the fabrication process can enhance carrier transport in hyperdoped-silicon-based solar cells and photodetectors.