Comparative Study of Properties of ZnO/GaN/Al₂O₃ and ZnO/Al₂O₃ Films Grown by Low-Pressure Metal Organic Chemical Vapour Deposition

ZnO films were deposited by low-pressure metal organic chemical vapour deposition on epi-GaN/Al₂O₃ films and c-Al₂O₃ substrates. The structure and optical properties of the ZnO/GaN/Al₂O₃ and ZnO/Al₂O₃ films have been investigated to determine the differences between the two substrates. ZnO films on GaN/Al₂O₃ show very strong emission features associated with exciton transitions, just as ZnO films on Al₂O₃, while the crystalline structural qualities for ZnO films on GaN/Al₂O₃ are much better than those for ZnO films directly grown on Al₂O₃ substrates. Zn and O elements in the deposited ZnO/GaN/Al₂O₃ and ZnO/Al₂O₃ films are investigated and compared by x-ray photoelectron spectroscopy. According to the statistical results, the Zn/O ratio changes from Zn-rich for ZnO/Al₂O₃ films to O-rich for ZnO/GaN/Al₂O₃ films.