Microstructure And Properties Of Ga-doped Zno Films Prepared By Pulsed Laser Deposition

ZnO film is a semiconductor material with excellent electric, optical and luminescence properties. Due to its excellent photoelectric property, ZnO thin film can be used in many photoelectric device such as thin film transistor (TFT), solar cell and laser device, etc. However, it is difficult to simultaneously get the excellent electric and optical properties for the undoped ZnO film. To enhance the specific application of ZnO film in optoelectronic devices, the electrical and optical properties can be judiciously tailored by appropriate doping. In this paper, the undoped ZnO films and Ga doped ZnO films (GZO) were prepared on silicon(100) and fused silica substrates by pulsed laser deposition. The effects of deposition parameters on the structure and properties of the films were investigated. The surface morphology, microstructure and crystal orientation of the deposited films were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The transmittance spectra, reflectance spectra, refractive index and extinction coefficient were measured using UV-VIS-NIR spectrophotometer and spectroscopic ellipsometer. The photoluminescence properties and mechanism of deposited films were also investigated by photoluminescence spectra.The GZO films grown at13Pa in oxygen atmosphere and600℃exhibited preferential orientation with c-axis perpendicular to the substrate surface. The calculated crystallize size and average surface RMS of GZO films decreased with increasing Ga dopant concentration. All the samples exhibited high transmittance about83%in the visible region. As the Ga dopant concentrations increased from0to8at.%, the optical band gap Eg values calculated from the transmittance spectra and reflectance spectra increased from3.26to3.33eV. The undoped ZnO film showed a typical and strong luminescence behavior of a narrow near band edge (NBE) emission without the deep level (DL) emission. For the GZO films, there was a DL emission besides the NBE emission.The GZO films exhibited a preferential c-axis orientation at the substrate temperature from300℃to600℃, and there was almost no effect of substrate temperature on the orientation. The GZO film grown at400℃demonstrated the largest crystallize size and the best crystal quality, while the GZO film grown at600℃showed the best photoluminescence property. These results indicated that the photoluminescence quality of the GZO film was not only dependent on the crystal quality. The GZO films grown at the oxygen pressure of3Pa and13Pa showed the preferential c-axis orientation. When the oxygen pressure was above23Pa, the structure of GZO films changed to polycrystalline structure without preferred orientation. With the decrease of oxygen pressure, the refractive index of GZO films increased, which resulted in the increase of stacking density. When the GZO films deposited at low and high oxygen pressure, the NBE emission peak was located around the same region, however, the origination of the NBE emission was different.