Al composition variations in AlGaN films grown on low-temperature GaN buffer layer by metalorganic chemical vapor deposition

We have investigated the optical properties of AlGaN grown on sapphire. It is found that two main luminescence peaks occur in the cathodoluminescence (CL) spectra of AlGaN films, and their energy separation increases with the increase of Al source flux during the growth. Spatially resolved CL investigations have shown that the line splitting is a result of variation of AlN mole fraction within the layer. The Al composition varies in both lateral and vertical direction. It is suggested that the difference in the surface mobility of Al and Ga atoms, especially, its strong influence on the initial island coalescence process and the formation of island-like regions on the uneven film surface, is responsible for the Al composition inhomogeneity. (C) 2008 Elsevier B.V. All rights reserved.

National Natural Science Foundation of China 60776047 605060016047602160576003National Basic Research Program of China 2007CB936700 National High Technology Research and Development Program of China 2007AA03Z401 The authors acknowledge the support from the National Natural Science Foundation of China (Grant nos. 60776047, 60506001. 60476021, and 60576003), the National Basic Research Program of China (Grant no. 2007CB936700) and the National High Technology Research and Development Program of China (Grant no. 2007AA03Z401).