The indium acceptor in Si, (ET-Ev)-270mV, was used as 4-micron infrared detector in satellite and space-craft applications since there is a atmospheric absorption window around this wavelength. The absorption cross section is about a Bohr radius of trapped hole. 10-16cm2. The solubility of indium in silicon crystal is about 1016cm-3.
The infrared photon flux is 1014cm-2s-1. How long would it take to detect 100 photons using an indium detector of 1 cm2area?