Characterization and properties of ZnO1-xSx alloy films fabricated by radio-frequency magnetron sputtering

A series of ZnO1-xSx alloy films (0 <= x <= 1) were grown on quartz substrates by radio-frequency (rf) magnetron sputtering of ZnS ceramic target, using oxygen and argon as working gas. X-ray diffraction measurement shows that the ZnO1-xSx films have wurtzite structure with (0 0 2) preferential orientation in O-rich side (O <= x <= 0.23) and zinc blende structure with (1 1 1) preferential orientation in S-rich side (0.77 <= x <= 1). However, when the S content is in the range of 0.23 < x < 0.77, the ZnO1-xSx film consists of two phases of wurtzite and zinc blende or amorphous ZnO1-xSx phase. The band gap energy of the films shows non-linear dependence on the S content, with an optical bowing parameter of about 2.9 eV. The photoluminescence (PL) measurement reveals that the PL spectrum of the wurtzite ZnO1-xSx is dominated by visible band and its PL intensity and intensity ratio of UV to visible band decrease greatly compared with undoped ZnO. All as-grown ZnO1-xSx films behave insulating, but show n-type conductivity for w-ZnO1-xSx and maintain insulating properties for beta-ZnO1-xSx after annealed. Mechanisms of effects of S on optical and electrical properties of the ZnO1-xSx alloy are discussed in the present work. (C) 2010 Elsevier B. V. All rights reserved.