Energy Shift of Native 2.45 eV Related Defects in Annealed ZnO Films

• Published in: IOP conference series. Materials Science and Engineering 2010-11, Vol.15 (1), p.012041-7
• Main Authors: Kondela, T, Greguš, J, Zahoran, M, Roch, T
• Format: Article
• Language: English
• Subjects: Annealing; Defect annealing; Excitons; Materials science; Optical properties; Oxidation; Oxide coatings; Oxygen; Photoluminescence; Sapphire; Scanning electron microscopy; Substrates; Vacancies; Zinc; Zinc oxide; Zinc oxides
• ISSN: 1757-899X; 1757-8981; 1757-899X
• DOI: 10.1088/1757-899X/15/1/012041

We study the influence of annealing temperature on the structural and optical properties of ZnO. Zinc oxide films were prepared by thermal oxidation of metallic Zn films. First, high quality (5N) Zn was evaporated onto sapphire substrate. Then zinc films were annealed in the oxygen atmosphere at several temperatures from 500 oC to 1100 oC. The surface was analyzed by Scanning Electron Microscopy (SEM) and structural properties were studied by XRD. Photoluminescence (PL) was measured from 350 nm to 800 nm, at two temperatures - 80 K and 300 K. Ordinary PL spectra could be divided into two parts. One band observed at ∼3.3 eV (UV PL) and second at 2.2 – 2.5 (VIS PL as "visible") - the maximum energy depends on annealing temperature. The origin of UV PL is in recombination of free excitons and bound excitons to donors and acceptors [1]. However, for VIS PL exact mechanism of emission recombination is still not fully understood. The main discussion is related to the native defects such as zinc vacancies or oxygen vacancies or oxygen antisite [2] but impurities like Cu [3] and/or hydrogen donors [4] are also candidates. Sample annealing temperature influenced the peak position of VIS PL and intensity of both part of the PL spectrum