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

Abstract

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 O 2 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 O 2 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.