SURFACE-MORPHOLOGY OF GAN FILMS DETERMINED FROM QUANTITATIVE X-RAY REFLECTIVITY

The surface of two GaN films grown under Ga-rich conditions by molecul ar beam epitaxy was characterized using x-ray reflectivity, assuming a self-affine/fractal surface morphology. The surface height fluctuatio ns were similar for both samples at the largest lateral length scales at which the fractal description is valid, although this lateral lengt h was significantly greater and the ''jaggedness'' significantly small er for the sample grown under higher Ga flux. Previous atomic force mi croscopy images revealed a higher density of large features on the sur face for the sample grown under lower Ga flux. The lateral size of the features are dominated by a convolution of the atomic force microscop y tip shape and the actual features on the surface, which precludes an accurate determination of the surface structure at length scales smal ler than the tip radius. This study illustrates the importance of usin g different techniques to evaluate the film surface morphology at diff erent length scales. (C) 1997 American Institute of Physics.