Improvement of Al-Polar AlN Layer Quality by Three-Stage Flow-Modulation Metalorganic Chemical Vapor Deposition

Improvement of Al-polar AlN layer quality was accomplished by three-stage flow-modulation metalorganic chemical vapor deposition (FM-MOCVD). In this method, the unit of the FM-MOCVD sequence was composed of three stages; Stage I for simultaneous source supply, Stage II for trimethylaluminum supply, and Stage III for ammonia supply, which were cyclically repeated. The AlN quality revealed by X-ray diffraction strongly depended on the time of Stage I. A growth model was proposed considering the surface coverage of the islands nucleated during Stage I. Exciton fine structures were eventually observed by low-temperature cathodoluminescence reflecting the tremendously improved crystalline quality.