The influence of Fe-doping on GaN grown on sapphire substrates by MOCVD was investigated using microscopy, in situ optical monitoring, double-crystal X-ray, Hall and photoluminescence. The growth from 3-D mode to 2-D mode for undoped GaN, and the growth from 2-D mode to 3-D mode for Fe-doped GaN was observed, respectively. The 2-D mode during the initial stage of the Fe-doped GaN buffer growth suggests that Fe plays a role of surfactant. A slight Fe-doping did not significantly degrade the crystalline quality of GaN buffer, confirmed by the FWHM of X-ray rocking curves. More than 4 orders of magnitude increase in the resistivity of Fe-doped GaN was achieved as compared to the undoped GaN. As a deep energy level acceptor, the compensation of Fe atom at the vacancy of Ga atom can be explained as the results of increased resistivity and suppressed yellow luminescence. (C) 2007 Elsevier B.V. All rights reserved.