High-temperature annealing effect of α-Al₂O₃ (0001) substrates with nominal 0.25° miscut toward the a-plane ${\mathbf{ \left( {11\overline{2} 0} \right)}}$ on ZnO films grown by MOCVD

Abstract

The annealing effects of c-plane sapphire (α-Al₂O₃) substrate with a vicinal-cut angle of α = 0.25° toward the a-plane $\left( {11\overline{2} 0} \right)$ on the quality of epitaxial ZnO films grown by metal organic chemical vapor deposition were studied. The atomic steps formed on sapphire substrate surface by annealing at high temperature were analyzed by atomic force microscopy (AFM). The annealing effects of sapphire substrate on the microstructural and optical properties of the ZnO films were examined by high-resolution X-ray diffraction, scanning electron microscopy, AFM and photoluminescence spectroscopy. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate. X-ray diffraction study revealed that ZnO films deposited on c-plane sapphire substrate annealed at T ≥ 1050 °C exhibit a wurtzite phase and have a c-axis orientation. The decrease in FWHM for (0004) and $\left( {10\overline{1} 4} \right)$ ZnO peak confirms the improvement of the crystalline quality of ZnO thin film as increasing annealing substrate temperature. Sapphire annealing at 1100 °C for 3 h under oxygen prior to ZnO film growth is the best to achieve ZnO film with good structural and optical quality.