Continuous order-disorder phase transition (2×2)→(1×1) on the (0001)AlN surface

Smooth (0001)AlN surface on a (0001) sapphire substrate was prepared by ammonia Molecular Beam Epitaxy. A continuous (2×2)(1×1) reconstruction phase transition on the (0001)AlN surface under ammonia flux was experimentally investigated by RHEED. The intensity of a fractional (0 1/2) streak was studied as a function of the sample temperature under different ammonia fluxes. The temperature of the transition increases with increasing of the ammonia flux (an effective activation energy is about 1.3 eV). The phase transition is described in the frame of the Bethe-Peierls approximation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)