Low Temperature Growth of ZnO Thin Films by Non-Equilibrium Atmospheric Pressure N₂/O₂ Plasma and the Growth Morphology of the Films

Abstract

The chemical vapor deposition system using non-equilibrium atmospheric pressure plasma was developed for the low temperature growth of ZnO films. As zinc source material, Bis (2,4-octanedionato) zinc which is free from spontaneous combustibility was selected. By introducing vaporized Zn(OD)₂ with carrier gas (nitrogen) and oxygen into discharging region, ZnO films was successfully obtained on the glass substrate at the substrate temperature as low as 200°C without using helium dilution of mixed gases. From XRD measurement, it was found that the films were well crystallized with (0001) preferred orientation. The films also showed high transmittance above 90% in visible region and sharp absorption edge at 3.31eV which corresponds to optical band-gap. The observation of cross-sectional morphology of samples revealed that the fabricated thin films typically have columnar grains with the diameter of approximately 20-30nm, and the grain size increases not only with increasing substrate temperature but also with increasing the vaporizing temperature of the Zn source materials.