Effect of crystalline polarity on microstructure and optoelectronic properties of gallium-doped zinc oxide films deposited onto glass substrates

The effect of crystalline polarity on the microstructure of gallium-doped zinc oxide (GZO) deposited using magnetron sputtering onto glass substrates was investigated. X-ray photoelectron spectroscopy was used to determine the crystalline polarity of c-axis textured GZO films. Grains whose radii were more than 1 μm grew abnormally in 0.2 mol% doped GZO when the film was thicker than ~ 1 μm, and the radius of the grains was much smaller than 100 nm in the heavily (i.e., 4 mol%) doped GZO, regardless of the film thickness. Such abnormal growth of the grains in the 0.2 mol% doped GZO films coincided with a change in the crystalline polarity: the surfaces of unusually large GZO grains were terminated with the (0001̄) face, and those of normal GZO grains were terminated with the (0001) face. The results indicated that polarity flipping is a very important event for controlling the texture of doped zinc oxide films.