Indium doped cadmium sulfide films deposited by cylindrical magnetron reactive sputtering

Abstract

Cadmium sulfide coatings about 500 nm thick were deposited by reactive sputtering onto borosilicate glass substrates at temperatures in the range 150°–350° C using pure and In-doped Cd cylindrical magnetron sputtering sources. The working gas was Ar–H2S with various H2S injection rates. Deposition rates were ∠1 nm/s. Adatom desorption was found to limit the cadmium sulfide accumulation rate to the extent to which the Cd could interact with the S to produce CdS. Consequently, the undoped deposits were nearly stoichiometric, with resistivities of ∠104 Ω cm. The resistivities of the doped coatings were found to be critically dependent on the H2S injection rate, apparently because of compensation by Cd vacancies. Resistivities in a range 0.1–5 Ω cm, suitable for Cu2S/CdS solar cells, were obtained for target doping levels of 0.1–1 at.% when the deposition flux was rich in Cd. Higher H2S injection rates yielded resistivities in the range 103 Ω cm. Electron Hall mobilities ranged from 2 to 15 cm2/V s in the doped CdS to 20 cm2/V s in the undoped material.