Effects of Growth Temperature on Properties of Nonpolar a-Plane ZnO Films on GaN Templates by Pulsed Laser Deposition

In this work, a-plane GaN/r-sapphire templates have been used to grow nonpolar a-plane ZnO films by pulsed laser deposition. The ZnO film growth temperature was varied in the range of 400A degrees C to 600A degrees C, and the effect of growth temperature on the properties of the ZnO thin films was investigated using x-ray diffraction, atomic force microscopy, photoluminescence (PL) spectroscopy, and Raman measurements. The results show that the crystal quality, surface morphology, strain states, and optical properties of a-plane ZnO films are strongly correlated with the deposition temperature. It is found that the crystallinity of the ZnO films gets better and the surface roughness decreases with increasing growth temperature. At a growth temperature of 600A degrees C, the a-ZnO films display the best crystal quality with x-ray (1120) omega scan full-width at half-maximum values of 0.28A degrees and 0.41A degrees on axis (1120) at azimuth 0A degrees and 90A degrees, respectively. Furthermore, the PL spectrum measured at 83 K is dominated by neutral donor-bound excitons and free-electron-to-bound (e-A (0)) emission, and relatively intense LO-phonon replicas of (e-A (0)) have also been observed in the a-plane ZnO. The dominance of the free exciton and the appearance of its replicas strongly indicate the high quality of the film.