Schönau, S.; Ruske, F.; Neubert, S.; Rech, B.: Annealing related changes in near-edge absorption and structural properties of Al-doped ZnO thin films. Physica Status Solidi C 11 (2014), p. 1468-1471
10.1002/pssc.201400002

Abstract:
In order to clarify the origin of the previously reported reduction of sub-band gap absorption of sputtered ZnO:Al films upon thermal annealing and raising deposition temperature, structural characterization using Raman spectroscopy was carried out on various films. Correlation of the Urbach energy to the FWHM of the E2(high) mode was found. Oxygen addition to the film growth did not result in changes of the Urbach energy, despite pronounced changes of the electrical properties. The results suggest that extended defects, rather than intrinsic point defects, give rise to the sub-band gap absorption.