Surface morphology of GaN films determined from quantitative x-ray reflectivity

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Abstract
The surface of two GaN films grown under Ga-rich conditions by molecular beam epitaxy was characterized using x-ray reflectivity, assuming a self-affine/fractal surface morphology. The surface height fluctuations were similar for both samples at the largest lateral length scales at which the fractal description is valid, although this lateral length was significantly greater and the “jaggedness” significantly smaller for the sample grown under higher Ga flux. Previous atomic force microscopy images revealed a higher density of large features on the surface for the sample grown under lower Ga flux. The lateral size of the features are dominated by a convolution of the atomic force microscopy tip shape and the actual features on the surface, which precludes an accurate determination of the surface structure at length scales smaller than the tip radius. This study illustrates the importance of using different techniques to evaluate the film surface morphology at different length scales.