Effects of oxygen-gas flow rate on lattice dynamics and microstructure for Ga-doped ZnO thin films prepared by reactive plasma deposition

The dependences of lattice constant, crystallite size and internal strain in the (100) direction for Ga-doped ZnO (GZO; Ga content, 3 wt%) films on O ₂ gas flow rate (0-20 sccm) during deposition were investigated. GZO films have been prepared by reactive plasma deposition (RPD). A series of GZO thin films with a thickness of 200 nm were deposited on glass substrate at 200 ^°C. In the range of O₂ gas flow rate from 0 to 10 sccm, from out-of-plane and in-plane X-ray diffraction (XRD) measurements, we find a large lattice constant of the c-axis and small changes in the lattice constant of the a-axis compared with those of undoped ZnO. This is in good agreement with the theoretical results for GZO crystals based on a model that the dominant defect is Ga at Zn sites (Ga_Zn). Excess O₂ gas flow increases both crystallite size and internal strain in the (100) direction and reduces the lattice constant of the c-axis for GZO films. This is caused by the formation of complex defects including n-type killers associated with vacant defects as determined by secondary-ion mass spectrometry (SIMS) and Raman spectroscopy.