Microstructure investigations of indium tin oxide films cosputtered with zinc oxide at room temperature

Abstract

X-ray diffraction coupled with atomic force microscopy measurements were employed to investigate the cosputtered oxide films at various zinc content [Zn∕(Zn+In)at.%] atomic ratios prepared at room temperature using rf cosputtering indium tin oxide (ITO) and zinc oxide (ZnO) targets simultaneously. The crystalline structure of a pure ITO film is polycrystalline with obvious diffraction peaks of (222) and (400). As the atomic ratio reaches 26%, the cosputtered oxide film evolves from a polycrystalline ITO structure into an amorphouslike ZnkIn2Ok+3 structure. This structure also dominates the cosputtered oxide films at the atomic ratios raging from 26% to 54%. The formation of amorphouslike ZnkIn2O3+k structures is found to markedly reduce the associated film resistivity and performs a superior surface uniformity. At an atomic ratio of 60%, a diffraction peak identifies as ZnO (100) phase appears to pile on the original amorphous domain. This phase is attributed to the substitution of In3+ sites in the ITO structure unit by Zn2+ ions. The appearance of ZnO phase is responsible for the increase of film resistivity. In addition, the smooth surface roughness contributed from the amorphous structures is therefore roughened due to the appearance of the microcrystalline ZnO structures. While the atomic ratio increases to 71%, the surface roughness and resistivity are found to further increase due to the growth of ZnO (100) phase. The optical absorption edge of these cosputtered oxide films shows an apparent redshift at ultraviolet wavelengths with incremental ZnO contents incorporating into ITO films.