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 O2 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 (GaZn). 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.