Bonding and Stoichiometry in Low Energy radio frequency magnetron Sputtered ZnO thin films on flexible Substrate

Abstract Spectroscopic and electrical studies of ZnO thin films grown by radio frequency magnetron sputtering at low power without substrate heating revealed improved stoichiometry and reduced free carrier concentration with increasingly energetic growth conditions, which is opposite to what is typically observed. Hall measurements showed a decrease in carrier concentration from 6.9 × 1019 cm−3 to 1.4 × 1019 cm−3 as power increased from 40 W to 120 W, and a decrease in carrier concentration from 8.6 × 1019 cm−3 to 2.6 × 1019 cm−3 as the deposition pressure decreased from 1.2 to 0.4 Pa. These findings correlated well with XRD, x-ray photoelectron spectroscopy and photoluminescence results, which showed that more energetic conditions increased the fraction of oxygen that was stoichiometrically bonded. The change in the absorption edge, likely due to a Burstein-Moss shift, was also in qualitative agreement. In the range of conditions used, energy transfer from the plasma to the growing film governs bonding, stoichiometry and hexagonal nanocrystalline film grain formation and growth.