Study on Solid-Phase Crystallization of Amorphized Vanadium-Doped ZnO Thin Films

Abstract

The effects of post-annealing and film thickness on the solid-phase crystallization (SPC) of amorphized vanadium-doped ZnO (VZO) thin films were investigated. The 2–500-nm-thick VZO (V of about 4 at.%) thin films were deposited on a c-face sapphire substrate at room temperature by RF magnetron sputtering and subsequently were annealed at an annealing temperature (TA) from 700°C to 900°C in a nitrogen atmosphere. From in-plane x-ray diffraction (XRD) measurements, the as-deposited VZO film had a faint in-plane orientation at the initial stage of deposition. However, the ZnO(100) XRD intensity weakened with increasing film thickness and no diffraction peak was seen over 35-nm thick. That is, the pseudo-amorphous film was fabricated. By annealing the 100-nm-thick VZO film over 700°C, the sixfold symmetry appeared. The ZnO(100) XRD intensity increased sharply at a TA of 800°C and was saturated at a higher TA. The c axis orientation reached a peak at a TA of 800°C according to the ZnO(002) XRD intensity. Concerning the effect of film thickness in the case of TA = 800°C, both the in-plane and c axis orientation improved up to 100-nm thick and deteriorated over it. At a TA ≥ 850°C or film thickness ≥200 nm, where the c axis orientation was deteriorated, the secondary phase-like Zn3V2O8 was formed. As a result, it is found that the careful selection of the TA and film thickness is necessary to avoid the formation of secondary phase-like Zn3V2O8 to fabricate the high-quality buffer layer via SPC.