Enhanced redshift of the optical band gap in Sn-doped ZnO free standing films using the sol–gel method

• Published in: Journal of physics. D, Applied physics Vol. 42; no. 18; pp. 185002 - 185002 (5)
• Main Authors: Yung, K C, Liem, H, Choy, H S
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 21.09.2009; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Ii-vi semiconductors; Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids); Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics; Grain size; Raman spectra; Impurity density; Doping; Spectral line shift; Thin films; Tin additions; Energy gap; Optical properties; Free-standing film; Zinc oxide; Spin-on coating; Absorption spectra; Sol-gel process; Deep level
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/42/18/185002

The optical band gap in free standing transparent zinc oxide (ZnO) films using the sol-gel method was studied. The effect of Sn doping on grain size, vibrational structure and on the optical properties of ZnO films was investigated. Contrary to the common observation, the optical band gap of Sn-doped ZnO is red-shifted from 3.38 to 3.18 eV as the doping weight percentage is increased to 3%. The redshift of the optical band gap is due to the deep states in the band gap, and a change of ~0.2 eV can only be observed when a substrate is not used. This study illustrates that removal of interaction between film boundaries and substrate is essential for developing effective band gap-tunable ZnO thin films.