Violet and UV luminescence emitted from ZnO thin films grown on sapphire by pulsed laser deposition

Visible violet photoluminescence (PL) has been achieved at room temperature (RT) from ZnO films grown on sapphire (001) substrate by pulsed laser depo sition (PLD). Substrate temperatures of 200, 300, and 400 degrees C have be en used in an oxygen pressure of 1 mTorr during the PLD. As the oxygen pres sure for the thin film deposition increases over 20 mTorr ata substrate tem perature of 400 degrees C, the violet luminescence vanishes. Instead ultra- violet (UV) and green-yellow luminescence appear. The most intense UV and g reen-yellow luminescence is obtained from a sample grown in an oxygen press ure of 200 mTorr at 400 degrees C. It is concluded that the intensity of th e UV luminescence strongly depends on the stoichiometry of the film as well as the crystalline quality, while the violet PL is due to a defect level i n the grain boundaries of the ZnOx crystals. (C) 2000 Elsevier Science S.A. All rights reserved.