  Presently, silicon photonics requires photodetectors that are sensitive in a
broad infrared range, can operate at room temperature, and are suitable for
integration with the existing Si-technology process. Here, we demonstrate
strong room-temperature sub-band-gap photoresponse of photodiodes based on Si
hyperdoped with tellurium. The epitaxially recrystallized Te-hyperdoped Si
layers are developed by ion implantation combined with pulsed-laser melting and
incorporate Te-dopant concentrations several orders of magnitude above the
solid solubility limit. With increasing Te concentration, the Te-hyperdoped
layer changes from insulating to quasi-metallic behavior with a finite
conductivity as the temperature tends to zero. The optical absorptance is found
to increase monotonically with increasing Te concentration and extends well
into the mid-infrared range. Temperature-dependent optoelectronic photoresponse
unambiguously demonstrates that the extended infrared photoresponsivity from
Te-hyperdoped Si p-n photodiodes is mediated by a Te intermediate band within
the upper half of the Si band gap. This work contributes to pave the way toward
establishing a Si-based broadband infrared photonic system operating at room
temperature.
