Submicron structure and acoustic properties of ZnO films deposited on (100) InP by pulsed laser deposition

Abstract

Highly textured (001) ZnO films have been deposited on (100) InP by pulsed laser deposition without substrate degradation. For this, growth starts in high vacuum, 8×10–7 mbar, with the substrate heated to 350 °C and later the oxygen pressure is increased up to 10–1 mbar, at which optimum crystallinity is achieved. Using a KrF laser at a fluence of 4 J/cm2, a repetition rate of 10 Hz and a target to substrate distance of 6 cm, the film growth rate is 0.08 Å/pulse. The film bulk has a columnar structure. The typical x-ray diffraction full width at half maximum (FWHM) is 0.2°–0.24°, while the -rocking curve FWHM is in the 1°–3° range. The surface shows two growth regimes: for thickness below 200 nm a granular film surface is obtained, and above this thickness the film surface exhibits submicron sized hexagonal pyramids. The tops of the pyramids have steps with heights of about 10 Å. The ZnO grains are randomly oriented about the [100] InP direction. The phase velocity of the acoustic bulk phonons of the ZnO films is about 6100 m/s.