  Single-crystal silicon wafers were hyperdoped respectively by sulfur,
selenium, and tellurium element using ion implantation and nanosecond laser
melting. The hyperdoping of such chalcogen elements endowed the treated silicon
with a strong and wide sub-bandgap light absorptance. When these hyperdoped
silicons were thermally annealed even at low temperatures (such as 200~400 oC),
however, this extra sub-bandgap absorptance began to attenuate. In order to
explain this attenuation of absorptance, alternatively, we consider it
corresponding to a chemical decomposition reaction from optically absorbing
structure to non-absorbing structure, and obtain a very good fitting to the
attenuated absorptances by using Arrhenius equation. Further, we extract the
reaction activation energies from the fittings and they are 0.343(+/- 0.031) eV
for S-, 0.426(+/-0.042) eV for Se-, and 0.317(+/-0.033) eV for Te-hyperdoped
silicon, respectively. We discuss these activation energies in term of the bond
energies of chalcogen-Si metastable bonds, and finally suggest that several
high-energy interstitial sites instead of the substitutional site, are very
possibly the atomic structures that are responsible for the sub-bandgap
absorptance of chalcogen hyperdoped silicon.
