Mid-infrared absorptance of silicon hyperdoped with chalcogens via fs-laser irradiation

Silicon hyperdoped with heavy chalcogen atoms via femtosecond-laser irradiation exhibits strong broadband absorption. Understanding this absorption could enable applications for infrared detection and the intermediate band photovoltaic effect. In this work, we extend absorption measurements to wavelengths >14 μm using Fourier transform infrared spectroscopy and study sulfur-, selenium- or tellurium-hyperdoped Si before and after annealing. We find that the surface morphology of the sample significantly influences the extent of absorption into the mid-infrared wavelength range. Additionally, annealing decreases absorptance and yields features consistent with free carrier absorption emerge. From mid-infrared absorption, we place an upper bound of the chalcogen dopant energy levels.