Effect of high temperature thermal treatment of (100) γ-LiAlO₂ substrate on epitaxial growth of ZnO films by plasma-assisted molecular beam epitaxy

Non-polar ZnO thin films were fabricated on (100) γ-LiAlO₂ substrates by plasma-assisted molecular beam epitaxy. The effect of high temperature thermal treatment of substrate on the crystalline orientation and quality of ZnO thin film was investigated. The film grown on (100) γ-LiAlO₂ substrate without high temperature thermal treatment consists of domains of both polar and non-polar orientations as identified by the X-ray diffraction pattern. Using high temperature thermal treatment of substrate, the growth of polar ZnO has been suppressed effectively. Besides, high temperature thermal treatment of substrate improves the crystalline quality of epitaxial ZnO thin film, which exhibits a smaller full width at half maximum value of ZnO (101⁻0) diffraction peak and a weaker deep level emission of photoluminescence. The suppression of polar ZnO growth and the quality improvement of the epitaxial ZnO films are due to the improvement of surface morphology and roughness of the substrate upon high temperature treatment. - Highlights: • ZnO films are grown on (100) γ-LiAlO₂ by plasma-assisted molecular beam epitaxy. • ZnO film grown on (100) γ-LiAlO₂ without high temperature treatment is dual-oriented. • ZnO film grown on γ-LiAlO₂ thermally-treated at 900 °C for 1 h is almost (101⁻0) oriented. • High-temperature thermal treatment of substrate improves ZnO crystalline quality