X-ray scattering study on the structural evolution of AlN/sapphire(0001) films during radiofrequency sputter growth

We present an x-ray scattering study on the evolution of the growth mode, t he surface morphology, and the lattice strain of AIN/sapphire(0001) films d uring sputter growth. Aligned epitaxial planar layers with strain relaxed t o about 2% are nucleated during initial stage growth. As the film thickness increases to an effective "critical" thickness of approximately 250 Angstr om, the growth gradually crosses over to the less aligned island growth. As the growth crossover occurs, the growth front becomes substantially roughe r and the residual strain begins to relax. The cogrowth of the planar layer and the islands results in a nonuniform strain distribution.