Photoconductivity of Lead Selenide: Theory of the Mechanism of Sensitization

Abstract

The intrinsic, majority, and minority carrier models of photoconductivity are critically examined in terms of an experimental study of the effect of oxygen, sulfur, selenium, and the halogens on PbSe films. It is concluded that the only model adequately describing these experimental results is the following:Radiation is absorbed in the crystallites and produces a main-band electron transition. Recombination centers which exist in the film produce a very short photoconductive time constant in a nonsensitized film; at room temperature this time constant is so small in PbSe that no photoconductivity is observed. Treatment with oxygen introduces minority carrier traps which increase the majority carrier lifetime and enhance the photoconductive sensitivity, both at room temperature and at reduced temperatures. Similar treatment with sulfur introduces shallow electron traps, which are effective in increasing the majority carrier lifetime at -195\ifmmode^\circ\else\textdegree\fi{}C but not at room temperature. Selenium and the halogens do not introduce minority carrier traps effective at any temperature studied.