Observation of enhanced infrared photoresponse in forward-biased amorphous silicon p-i-n diodes

The photoconductive response of hydrogenated amorphous silicon (a-Si:H) p-i-n diodes has been investigated under conditions of low-temperature operation. We show that cooled p-i-n diodes exhibit an enhanced infrared response when operated under forward bias conditions. The induced IR response is of the order of 10−3A/W, extending out to wavelengths of about 2–3 μm with the long wavelength cutoff being determined by the properties of the glass/indium–tin–oxide entrance window. We propose that the IR photoeffect is due to the re-excitation of band-tail trapped excess carriers injected into the localized conduction and valence band tail states in the vicinity of the n+- and p+-contact regions.