Reactivation of sub-bandgap absorption in chalcogen-hyperdoped silicon

Abstract:

Silicon doped with non-equilibrium concentrations of chalcogens using a femtosecond laser exhibits near-unity absorption of sub-bandgap photons to wavelengths of at least 2500 nm. Previous studies have shown that sub-bandgap absorptance decreases with thermal annealing up to 1175 K, and that the absorption deactivation correlates with chalcogen diffusivity. In this work, we show that sub-bandgap absorptance can be reactivated by annealing at temperatures between 1350 K and 1550 K followed by fast cooling (> 50 K/s). Our results suggest that the defects responsible for sub-bandgap absorptance are in equilibrium at high-temperatures in hyperdoped Si:chalcogen systems.