Zinc oxide (ZnO) films have been deposited on 1 μm SiO2/Si (100) substrates by rf magnetron sputtering. Using a sputtering gas of pure oxygen, a pressure regime is found in which the ZnO films grow on room temperature substrates with a single (0001) orientation, small grains (crystallite sizes ∼10–15 nm), and high intrinsic biaxial compressive stress (∼6 GPa). The effects of post-deposition annealing these films in air was investigated over a range of temperatures (200–1000 °C) and durations (2–2000 min). Annealing resulted in lower biaxial compressive stresses and increased average crystallite sizes in all films. Additional ZnO grain orientations were detected only after annealing above 500 °C for longer than 90 min, and the results are interpreted in terms of film recrystallization. Consequently, a relatively rapid thermal anneal at 1000 °C for 5 min caused grain recovery without recrystallization, resulting in maximum stress reduction (90%–100% of stress was relieved and average crystallized size tripled) while maintaining the original film orientation. The film surface area—measured by atomic force microscopy—decreased by up to 25% during annealing. X-ray photoelectron spectroscopy results indicate that although the surfaces of as-deposited films have a slight excess of oxygen, annealing as low as 200 °C results in a stoichiometric ZnO surface. High values of electrical resistivity (∼105 Ω cm) measured across the thickness of unannealed oriented films indicate low levels of elemental zinc clusters in the film bulk.

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The coupling efficiencies of sputtered, c-axis-orientated zinc oxide (ZnO) films in guided wave resonance optical modulators have been measured. The ZnO planar waveguide is sandwiched between two 3 nm thick chromium layers on top of a Si02p(100) substrate. This novel design facilitates application of a modulation voltage directly across the dielectric film in a prism coupler set-up and thus avoids voltage losses across the silicon dioxide (SO,) optical isolation layer.We present a comparison of four differently prepared ZnO waveguideslmodulators to investigate the influence of film crystallinity on the coupling efficiency and electro-optical parameters. The coupling efficiency of a ZnO waveguide is found to be dependent on both film thickness and average grain diameter measured in the plane of the film. A high efficiency (0.76) can be achieved for film thicknesses below 300 nm when the average grain diameter is 26 nm. This value is comparable to the maximum value of tvDicallv around 0.

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