Sputter deposition of Cd1−x Znx S photoconductive films

An rf-sputtering technique has been developed for the deposition of Cd1−x Znx S photoconductive films to be used in light valve display devices. Targets of CdS containing 19, 29, 49, and 70 mole% ZnS have been used. Thermally sensitive and stress-sensitive substrates necessitated that deposition conditions be adjusted for each of the targets. To help maintain film stoichiometry, an Ar+1% H2S sputtering gas was used at a throughput of about 0.3 Torr liter/sec. In order to minimize contamination of the deposited film and to reduce film buildup in the chamber, a glass ring concentric with the target was used to confine the discharge. With a given target, it was possible to alter the Cd/Zn ratio in the film by altering the sputtering conditions and thus controlling the spectral sensitivity over a limited range. Films were routinely deposited with maximum photoconductivity occurring within a range of 1.0–2.0 nm about 435 nm. Dark resistivity and photoconductive gain as well as stress level in the coated substrate were found to be highly reproducible.