We studied the morphological dependence of the initial GaN seed layers on in situ deposited SixNy and its effect on the structural and electrical properties of GaN epilayers overgrown by low-pressure metalorganic chemical vapor deposition. Primarily scanning electron microscopy images were used for a systematic investigation of the effects of the growth parameters of SixNy and GaN layers on the morphology of the initial GaN seed layers prior to overgrown layers. High-resolution X-ray diffraction measurements revealed that the full width at half maximum of (102) rocking curve decreased significantly from 8.4 to 4.6 arcmin as the chamber pressure was increased from 30 to 300 Torr for the growth of the 0.3 mu m-thick initial GaN seed layer. Thermally activated carrier transport measurements in the overgrown GaN epilayers showed a V-shaped temperature-dependent electron concentration profile with a minimum at 80 K, the shape of which is attributed to a highly degenerate impurity band in the heavily silicon-doped GaN region at the GaN/SixNy interface. (c) 2006 Elsevier B.V. All rights reserved.