Semiconductor infrared photodetectors

A semiconductor device capable of enhanced sub-bandgap photon absorption and detection is described. This semiconductor device includes a p-n junction structure formed of a semiconductor material, wherein the p-n junction structure is configured such that at least one side of the p-n junction (p-side or n-side) is spatially confined in at least one dimension of the device (e.g., the direction perpendicular to the p-n junction interface). Moreover, at least one side of the p-n junction (p-side or n-side) is heavily doped. The semiconductor device also includes electrical contacts formed on a semiconductor substrate to apply an electrical bias to the p-n junction to activate the optical response at target optical wavelength corresponds to an energy substantially equal to or less than the energy band-gap of the first semiconductor material. In particular embodiments, the semiconductor material is silicon.