Gallium nitride (GaN) thin films were grown on (0001) sapphire using a direct reaction of NH3 (ammonia) and metallic Ga (gallium) diluted with metallic Bi (bismuth) in a conventional resistance heated reactor. The growth of GaN thin films was carried out for 6 h at 750degreesC under low pressure. In this study, the flow rate or NH3 was varied from 10 to 100 seem. The crystallinity, optical and electrical properties of the GaN films were measured to investigate the NH3 flow rate dependence of the films grown. The NH3 flow rate influenced the quality of the GaN thin films. At the NH3 flow rate of 60 seem, we obtained a good quality of GaN films which exhibited a full width at half maximum of 10 arcmin from the X-ray rocking curve, a neutral-donor bound exciton (I-2 line) emission in 13 K photoluminescence (PL), an electron mobility of 45 cm(2)/V-s and concentration of 2 x 10(19) cm(-3) at 300 K. (C) 2002 Elsevier Science B.V. All rights reserved.