THE AG PHOTODOPING MECHANISM IN AS2S3

We have measured the number of photons/cm2 over the energy range 1.95 to 3.35 eV, required to form a negative-relief image in 2000 angstrom films of As2S3 using 100 angstrom films of evaporated Ag, Ag2Te, Ag2Se, and AgBr. We have observed sensitivity below the band gap of As2S3 in all cases. We have observed an increase in sensitivity by several orders of magnitude with increase of photon energy between 1.95 and 3.35 eV. The sensitivity decreases from Ag to the semimetals Ag2Te and Ag2Se to the wide band gap AgBr by the ratio 1:50:2500 at 2.4 eV. Assuming an internal photoemission model as proposed by Goldschmidt and Rudman, we extract barrier heights of 1.71, 2.10, 2.22 and 2.42 eV for Ag, Ag2Te, Ag2Se, and AgBr.