Optimization of photoconductivity in vacuum-evaporated tin sulfide thin films

Annealing in air and argon each produces an increase of a factor of 5 or more in the photoconductivity/dark conductivity ratio (Gph/Gdark) of vacuum-evaporated tin sulfide (SnS) thin films on glass substrates with copper contacts. No significant increase in Gph/Gdark is observed after annealing SnS thin films with silver contacts. Annealing in air at or above 250 °C for 5 min dramatically increases the dark conductivity of the films. Annealing in Ar produces no significant increase in dark conductivity. It is probable that the rise in dark conductivity that accompanies annealing in air is caused by thermal activation of oxygen acceptors followed at higher temperatures by the conversion of SnS to SnO2. The films display photoconductivity from the near-infrared to the ultraviolet. The thinnest films we have produced (18 nm) display the highest Gph/Gdark and are three times more photoconductive at 400 nm than they are at 700 nm.