The N-polar GaN grown on c-plane sapphire with an indium-facilitated growth technique by RF-MBE has been studied. Upon the incorporation of indium during growth, the photoluminescence intensity and electron mobility of GaN have been enhanced by a factor of 15 and 6, respectively. The electron concentration drastically increases by several orders of magnitude. The biaxial strain of GaN film estimated with micro-Raman technique reduces from 0.6729 to 0.5044 GPa. The full-width at half-maximum of asymmetric (10 (1) over bar2) X-ray reflection which related to the density of overall threading dislocations (TDs) increases from 593 to 744 arcsec. In contrast, the symmetric (0002) reflection related only to TDs having a non-zero c-component Burgers vectors reduces from 528 to 276 arcsec. The enhancement of GaN optical property is generally attributed to the reduction of non-zero c-component dislocations. The reduction in density is confirmed by cross-sectional transmission electron microscopy. (C) 2003 Elsevier B.V. All rights reserved.