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, the surface morphology, and the lattice strain of AlN/sapphire(0001) films during sputter growth. Aligned epitaxial planar layers with strain relaxed to about 2% are nucleated during initial stage growth. As the film thickness increases to an effective “critical” thickness of approximately 250 Å, the growth gradually crosses over to the less aligned island growth. As the growth crossover occurs, the growth front becomes substantially rougher and the residual strain begins to relax. The cogrowth of the planar layer and the islands results in a nonuniform strain distribution.