Effects of ZnO composition on structure, optical and electrical properties of cosputtering In₂O₃–Ga₂O₃–ZnO films

This study investigated the impacts of structure, optical and electrical properties of indium–gallium–zinc oxide (IGZO) film with varied ZnO deposition powers on glass substrates by using cosputtering system with two radio-frequency (RF) (ZnO and Ga₂O₃) and one direct-current (DC) (In₂O₃) magnetron. The average transmittance decreased obviously from 86.37 to 81.44 % and the optical energy gap decreased from 3.56 to 3.29 eV when ZnO deposition power increases. Results are ascribed to facts that the content of Zn in IGZO films was increased and the fitting extinction coefficient near the wavelength in the range of 370–450 nm obviously increased with increase of ZnO deposition power; the fitting refractive index of IGZO films was noticeably increased and surface morphology displayed a dense structure. The crystallinities of IGZO films reveal from an amorphous structure with a content of Zn less than 50 at.% to a polycrystalline phase of IGZO film with a content of Zn around 70.5 at.%. The residual stress of the indium gallium oxide (IGO) films with undoped ZnO content significantly changed from a tensile stress to a compressive stress with an increased annealing temperature. When the ZnO composition incorporated into the IGO film, variations of the residual stress in the films gradually become smaller. The optimum process condition of cosputtering IGZO films with a ZnO deposition power at 100 W and an annealing temperature at 300 °C showed the largest film mobility, smallest surface roughness, and a lower residual stress.