Çörekçi, S.Öztürk, M. K.Bengi, A.Çakmak, M.Özçelik, S.Özbay, Ekmel2016-02-082016-02-082010-10-230022-2461http://hdl.handle.net/11693/22015An AlN buffer layer and a thick-GaN layer for high-electron-mobility transistors (HEMTs) were grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The structural and morphological properties of the layers were investigated by high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) techniques. The optical quality of the thick-GaN layer was also evaluated in detail by a photoluminescence (PL) measurement. It was found that the AlN buffer layer possesses high crystal quality and an atomically flat surface with a root-mean-square (rms) roughness of 0.16 nm. The screw-and edge-type dislocation densities of the thick-GaN layer were determined as 5.4 9 107 and 5.0 9 109 cm-2 by means of the mosaic crystal model, respectively. It was observed that the GaN layer has a smooth surface with an rms of 0.84 nm. Furthermore, the dark spot density of the GaN surface was estimated as 6.5 9 108 cm-2 over a scan area of 4 μm2. © Springer Science+Business Media, LLC 2010.EnglishAtomically flat surfaceCrystal qualitiesDark spotsDislocation densitiesGaN layersHigh-resolution x-ray diffractionMosaic crystal modelOptical qualitiesPhotoluminescence measurementsRoot mean square roughnessArticle10.1007/s10853-010-4973-7