Effect of oxygen on the physical parameters of RF sputtered ZnO thin film

ZnO films were grown using an RF sputtering technique and a hot-pressed oxide target. Glass and single-crystal silicon substrates were used. The substrate temperature T s was varied from room temperature (300 K) to 625 K. The sputtering ambient was argon and 80% argon+20% oxygen gas mixture. At room temperature the films grown in pure argon showed good c axis orientation for both glass and Si substrates, i.e. reflections from the (002) plane. The strong reflections of the (100) and (101) planes show up with the introduction of the oxygen at room temperature, and they remain dominant even when the substrate temperature is increased to 373 K. However, with a further increase in substrate temperature to 625 K the films become highly oriented to the c axis. The change in grain size and lattice constants with sputtering parameters (especially substrate temperature) can be explained by assuming incorporation of oxygen neutrals at low substrate temperatures and their out-diffusion at high substrate temperatures. The effect of sputtering parameters on the electrical conductivity and optical band gap are also reported.