Highly c-Oriented Nanocolumn Structure ZnO Films on Sapphire Substrates by Pulsed Laser Deposition

Highly c-oriented nanocolumn structure ZnO films were successfully deposited on sapphire (0001) substrates by pulsed laser deposition at a substrate temperature of 500°C and 200 mTorr oxygen pressure. X-ray diffraction, scanning electron microscopy, photoluminescence, and spectroscopic ellipsometry were used to characterize the ZnO films. The as-grown film is composed of well-aligned ZnO columns with diameters about 200-300 nm. Photoluminescence spectrum of the ZnO film exhibits a strong near-band-edge emission and a weak deep-level emission band. The optical refractive indices and the extinction coefficients are obtained by fitting the spectroscopic ellipsometry data using the Forouhi-Bloomer dispersion relation.