Transport phenomena in high performance nanocrystalline ZnO:Ga films deposited by plasma-enhanced chemical vapor deposition

Nanocrystalline gallium doped zinc oxide (ZnO:Ga) thin films were synthesized by plasma-enhanced chemical vapor deposition (PECVD). A statistical design of experiments (DOE) was employed to optimize electrical conductivity. A carrier concentration of 5.5 x 10(20)/cm(3) and a mobility of 15 cm(2)/V s yielding a resistivity of 7.5 x 10(-4) Omega cm resulted from the conditions of high pressure, rf power, and electrode gap. X-ray diffraction showed that gallium doping had a profound impact on film orientation. Atomic force microscopy (AFM) revealed that the films were nanostructured, with an average grain size of 80 nm and a surface roughness of similar to2 nm. This unique morphology benefited optical transmission, but limited electrical performance. Average transmission across the visible spectrum was similar to93% as scattering losses were minimized. Temperature dependent Hall and optical transmission measurements demonstrated that structural defects and ionized impurities were equal contributors to electron scattering. (C) 2004 Elsevier B.V. All rights reserved.