GaN layers were grown by ammonia molecular beam epitaxy (NH3 MBE) on rf plasma MBE (rf-MBE) AlN grown on (110) Si substrates. The surface morphology of GaN epitaxial films is sensitive to the V/III ratio with the RHEED transition from 2D to 3D as NH3 beam equivalent pressure (BEP) increases. The measured FWHMs of X-ray rocking curve for slightly N-rich sample of 0.8 mu m thick are 665 and 961 arc-sec for (0002) and (10 (1) over bar2) peaks, respectively. Based on transmission electron microscopy studies, the reduction in rocking curve width is attributed to enhanced annihilation of dislocations during the initial stage of growth, which agrees with much higher luminescence intensity in room-temperature cathodoluminescence measurements. A kinetic growth model based on the reference [jae.] is used to explain the growth behavior of GaN layers with different NH3 BEP. (C) 2013 Elsevier B.V. All rights reserved.