Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

• Published in: Thin solid films 2011-04, Vol.519 (13), p.4366-4370
• Main Authors: Yu, Chung-Jong, Sung, Nark-Eon, Lee, Han-Koo, Shin, Hyun-Joon, Yun, Young-Duck, Kang, Seen-Woong, Lee, Ik-Jae
• Format: Article
• Language: English
• Subjects: Carrier density; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Deposition by sputtering; Diffraction; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Epitaxy; Exact sciences and technology; Extented X-ray absorption fine structure spectroscopy; Film thickness; Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects); Hall-effect measurement; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Orientation; Physics; Spectra; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Theory and models of film growth; Thin film structure and morphology; Thin films; X-ray absorption near-edge structure spectroscopy; X-ray diffraction; X-rays; Zinc oxide
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2011.02.009

The epitaxial growth of ZnO thin films on Al 2O 3 (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10 19 cm − 3 , 24.62 cm 2V − 1 s − 1 , and 1.38 × 10 − 2 Ω cm, respectively.