Surface morphology and crystalline structure of sequentially sputtered ZnO nanocoatings

The sequential sputtering technology was developed for the formation of transparent and conductive ZnO ultrathin films (doped by Al, Ga) of thicknesses about 100 nm. When comparing continuous and sequential deposition modes, the latter increased the preferential [0 0 1] columnar texture of ZnO:(Ga, Al) films, lowered their grain and crystallite sizes (25 nm/40 nm and 33 nm/47 nm), lattice stress gradients (0.147 GPa nm−1/0.180 GPa nm−1) and microstrains (8.4 × 10−3/5.6 × 10−3), rose their transmitance in Vis/NIR region (above 80%) and decreased their refractive index (values below 2). Post-deposition annealing of sequentially sputtered films in vacuum at 400 °C shifted their transmittance to the shorter wavelength in UV region and increased refractive index to values above 2.