Five GaN films grown by metal-organic chemical vapor deposition (MOCVD) method were investigated. The growth was performed using a home-made vertical reactor operating at atmospheric pressure. The growth was carried out on (0001) oriented sapphire substrates using trimethylgallium(TMGa) and blue-ammonia(NH

3

) as Ga and N sources

respectively. The mixed gases of hydrogen and nitrogen were used as the carrier gases. A thin buffer layer with thickness of about 15nm was grown at 520℃ and recrystallized at 1060℃ for 6 minutes. The GaN films were grown at 1060℃.Optical transmission measurement

photoluminescence (PL)

double-crystal X-ray diffraction (DCXRD) and the Van der Pauw Hallmethod were used to measure the optical

structural and electrical data of these films at room temperature.Table 1 gives the characterization data of the five GaN films.Fig. 2 shows the optical transmission spectra of GaN films. The optical absorption edge of GaN films is at 366nm.The transmittance varies between 63% and 93% for the used samples.Fig. 3 shows the relationship between the FWHM of double-crystal X-ray diffraction (DCXRD) and transmittance. As shown in Table 1

the FWHM of DCXRD becomes smaller when transmittance increases

which suggests that the higher the transmittance

the better the crystal quality.Fig. 4 shows the photoluminescence (PL) spectra of five GaN films at 300K. The excitation-source was a 15mW He-Cd laser. The peaks of band-edge emission of Samples B

D and E were very sharp. The band-edge emission intensity of Sample A was very weak

but its FWHM of DCXRD was the smallest

which indicates that the optical property of GaN determined by PL isn' t in correspondence with the crystal quality determined by DCXRD.The experimental results show that the crystalline quality of GaN determined by transmission measurement is in agreement with that determined by DCXRD. But we did not observe the same relationship in PL spectra with DCXRD. This paper also reports that a highly resistive GaN film grown by atmospheric pressure MOCVD has RBS/channeling yield x

min

of 1.5%.