GaN growth on nitridated sapphire (0001) by rf plasma-assisted metal-organic molecular-beam epitaxy is shown to exhibit a highly superlinear growth rate and a transition from strained, smooth growth to relaxed cluster growth during the first layer. A coupled rate-equation model suggests that the growth rate arises from both the site-dependent reactivity of precursor molecules and a layer-dependent interlayer transport probability. The nitridation layer, which determines the initial strain of the GaN film, bears a striking resemblance to a well known Al-rich surface reconstruction of sapphire.

• Received 17 June 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.4349