Photoconductivity in Lead Selenide. Experimental

Abstract

The electrical and photoconductive properties of evaporated films of PbSe have been investigated using oxygen, sulfur, selenium, and the halogens as sensitizers. Each sensitizer acts as an acceptor impurity; increasing sensitizer concentration causes the film resistance to increase through a maximum and then decrease, the film changing from $n$ to $p$ type at the resistance maximum. Photoconductivity at room temperature could be produced only by treatment with oxygen; the time constant $\ensuremath{\tau}$ was of the order of 1 \ensuremath{\mu}sec. At -195\ifmmode^\circ\else\textdegree\fi{}C photoconductivity ($\ensuremath{\tau}=15 \mathrm{to} 30$ \ensuremath{\mu}sec) could be produced by any of the sensitizers, while oxygen treatment gave in addition a response with $\ensuremath{\tau}\ensuremath{\sim}5$ msec. The spectral response extends to longer wavelengths in thick films than in thin films, but is independent of sensitizer used. It is concluded that oxygen introduces acceptor levels which are minority carrier traps, while the other sensitizers introduce acceptor levels which are not effective minority carrier traps.