Characteristics of nano-laminated al-doped ZnO (AZO) multilayers

The structural, morphological, optical, and electrical properties of Al-doped ZnO (AZO) single layer and AZO/metal (Ag and Au: 3 nm)/AZO multilayer thin films prepared via sputtering processes were characterized. Additionally, the effect of post-annealing on the properties of films was investigated. X-ray diffraction revealed that the crystal properties of hexagonal wurtzite crystal structures and the preferred orientation of ZnO (002), with c-axis growth for both AZO single layer and AZO multilayer films. Surface roughness was not degraded by inserting metals into the AZO films. Post air annealing at 300°C improved the crystallinity and surface roughness of the films. AZO multilayer films exhibited lower transmittance values compared with AZO single layer films, but improved after post-annealing. The energy band gap was about 3.5 eV for the AZO multilayer films. Compared to AZO single layer films, AZO multilayer films exhibited lower sheet resistance and resistivity values. Additionally, high carrier concentrations and electron mobilities were attained by inserting metals into AZO. Post-annealing further improved the electrical properties. The post-annealed AZO/Ag/AZO thin films exhibited the best properties (4.26 × 10^-3 Ω^-1) as Haccke figure of merit (FOM) parameters, due to low sheet resistance (6.75 Ω/sq) and moderate transmittance (70.12%) within the visible light region.