Optimization of Laser Energy Fluence in Pulsed Laser Deposition of ZnO on Al 2 O 3 (0001)

The effects of laser energy fluence on the growth of pulsed laser deposited ZnO thin films on c -plane sapphire substrates were systematically investigated by using x -ray diffraction, Rutherford backscattering spectrometry with ion channeling, and scanning electron microscopy techniques. Optical and electrical properties of the ZnO epilayers were characterized by using ultraviolet-visible transmission spectroscopy and Van der Pauw measurements, respectively. It was found that the laser fluence has strong effects on the crystalline, optical and electrical qualities of the ZnO films. At low laser fluence, ZnO film grows via 3D-island mode with low deposition rate, loss of Zn near the surface and particulates on top of the film. High laser fluence may also cause simultaneous multi-layer growth and the degradation of crystalline, electrical, and optical quality of the ZnO films. The optimal laser fluence window was found between 1.2J/cm 2 and 2.5 J/cm 2 for obtaining high quality ZnO films for optoelectronic applications. The dependence of laser fluence on the ZnO growth mode, surface morphology and electrical and optical properties is discussed.