Yu, H.Ozturk, K. M.Ozcelik, S.Özbay, Ekmel2016-02-082016-02-0820060022-0248http://hdl.handle.net/11693/23751We report the remarkably improved crystal quality of semi-insulating GaN grown by metalorganic chemical vapor deposition on an AlN buffer layer, which is deposited on sapphire substrate. The electrical and structural properties are characterized by dark current-voltage transmission line model and X-ray diffraction measurements. It is found that the crystal quality of the GaN epilayer is strongly related with the growth temperature of the decreased-temperature GaN interlayer. In comparison with the normal GaN grown on sapphire, the crystal quality is remarkably improved along with a semi-insulating electrical character. The high-mobility field effect transistors device based on the semi-insulating GaN shows good pinch off properties. Our electrical measurement results of GaN grown directly on an AlN buffer indicated that the as-grown-undoped GaN is naturally semi-insulating material. The origination of the residual donors in normal GaN grown on sapphire substrate is also discussed.EnglishA1. DislocationA1. X-ray diffractionA3. AlN bufferA3. MOCVDB1. III-V nitridesArticle10.1016/j.jcrysgro.2006.05.0561873-5002