Browsing by Author "Yu H."
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Item Open Access Experimental study of two-step growth of thin AlN film on 4H-SiC substrate by metalorganic chemical vapor deposition(2010) Yu H.; Ozturk, M.; Demirel P.; Cakmak H.; Buyuklimanli, T.; Ou W.; Özbay, EkmelWe report growth optimizations of the thin AlN film on (0001) 4H-SiC substrates by metalorganic chemical vapor deposition. The influence of growth conditions, such as growth temperature and the V/III molar ratio, on the material quality of AlN film is studied. The surface morphology and crystalline quality of the epitaxial layers are investigated by atomic force microscope, X-ray diffraction, and transmission electronic microscope. A new approach is demonstrated to improve the crystalline quality of a 100 nm-thick AlN film by the use of a 5 nm-thick low temperature AlN nucleation layer. Compared to a conventional AlN layer directly grown on SiC substrate at high temperature, the surface morphology of two-step AlN film is remarkably improved along with a decreasing of defect density, leading to the improvement of crystalline quality for the subsequently grown GaN layer. The mechanisms of crystalline quality improvement by use of a low temperature AlN nucleation layer are also investigated and discussed.Item Open Access Growth of high crystalline quality semi-insulating GaN layers for high electron mobility transistor applications(2006) Yu H.; Caliskan, D.; Özbay, EkmelSemi-insulating character (sheet resistivity of 3.26 × 10 11 Ω/sq) of thick GaN layers was developed for AlGaN/GaN high electron mobility transistor (HEMT) applications on an AlN buffer layer. Electrical and structural properties were characterized by a dark current-voltage transmission line model, x-ray diffraction, and atomic force microscope measurements. The experimental results showed that compared to semi-insulating GaN grown on low temperature GaN nucleation, the crystal quality as well as surface morphology were remarkably improved. It was ascribed to the utilization of a high quality insulating AlN buffer layer and the GaN initial coalescence growth mode. Moreover, the significant increase of electron mobility in a HEMT structure suggests that this is a very promising method to obtain high performance AlGaN/GaN HEMT structures on sapphire substrates. © 2006 American Institute of Physics.