Control and characterization of ZnO/GaN heterointerfaces in plasma-assisted MBE-grown ZnO films on GaN/Al2O3

We report control of ZnO/GaN heterointerface by employing pre-treatments pr ior to ZnO films growth. Interface layer formation at ZnO/GaN heterointerfa ce and control of interface laver formation was investigated. Interface lay er was formed by first oxygen pre-exposure about 2-8 min to the Ga face (00 01) GaN/sapphire substrate. The interface layer was observed directly by hi gh-resolution transmission electron microscopy (HRTEM) and identified as a single crystalline monoclinic Ga2O3. ZnO film on the interface layer was si ngle crystal. The formation of the oxide interface layer was prevented by f irst pre-exposure of zinc. Over-exposure (about 15 min) to oxygen plasma re sults in amorphous layer evaluated by reflection high-energy electron diffr action (RHEED) observation. Even on this surface, further ZnO films were gr own as a single crystal as confirmed by RHEED and HRTEM observations. Howev er, amorphous layer on the top of the interface layer was not observed by H RTEM. We concluded that the amorphous layer might be transformed to crystal line layer during ZnO growth by solid phase epitaxy. (C) 2000 Elsevier Scie nce B.V. All rights reserved. PACS: 68.35.Ct: 81.05.Dz; 81.05Ea: 81.15.Hi; 81.15.Gh.