Effect of a ZnO buffer layer on the properties of epitaxial ZnO:Ga films deposited on c-sapphire substrate

Abstract Bi-layer ZnO films with 2 wt.% Al (AZO; ZnO:Al) and 4 wt.% Ga-doped (GZO; ZnO:Ga) were deposited on the non-buffered and buffered c(0 0 0 1)-sapphire(Al 2 O 3 ) substrates respectively by Pulsed Laser Deposition (PLD). The effect of a ZnO buffer layer on the crystallinity and electrical properties of the GZO thin films was investigated. X-ray Diffraction (XRD) peaks and High Resolution Transmission Electron Microscopy (HRTEM) studies showed that the GZO thin film on a buffered substrate was epitaxially grown with an orientation relationship of (0 0 0 1) [ 1 1 2 ¯ 0 ] GZO | | ( 0 0 0 1 ) [ 1 1 2 ¯ 0 ] Al 2 O 3 . However, GZO thin film on a non-buffered substrate was grown as a monocrystalline hexagonal wurtzite phase with c -axis preferred, out-of-plane orientation, and random in-plane orientation. The electrical resistivity of the GZO thin films was improved by introducing a ZnO buffer layer from 2.2 × 10 -4  Ω cm to 1.2 × 10 -4  Ω cm, respectively. In a word, it was found in the films that more preferred c -axis orientation texture and reduction of the defects such as stacking faults and dislocations, with introducing a ZnO buffer layer. It was seen that the ZnO buffer layer had a great influence on the orientation and defect density of GZO thin films from X-ray Diffraction (XRD) peaks and High Resolution Transmission Electron Microscopy (HRTEM) images.