Papers by Author: Geun Hyoung Lee

Abstract: TiO2 thin films were deposited on both bare Si and Si substrates with ZnO buffer layer (ZnO/Si) by radio frequency (rf) magnetron sputtering of TiO2 target at a substrate temperature of 500
. A mixed gas of Ar and O2 was used for sputtering and O2 flow ratio was changed from 0 to 30%. X-ray diffraction patterns showed that the TiO2 thin films had only rutile structure. The weak diffraction peak from the (110) plane of rutile structure was observed for the TiO2 film formed on bare Si substrate. For the TiO2 film on ZnO/Si, the diffraction peak from the (200) rutile structure was dominant. The diffraction intensity from the rutile structure of TiO2/ZnO/Si was stronger than that of TiO2/Si. This implies that ZnO buffer layer promoted the crystallization of rutile structure.

Abstract: SiC single crystal ingots grown by sublimation physical vapor transport (PVT) technique were prepared and then the SiC crystal quality with varying crucible design employing a guide tube and tantalum foil was systematically investigated. The growth rate of 2-inch SiC crystal grown by these crucible designs was about 0.3 mm/hr. The n-type and p-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC were successfully fabricated. The doping concentration level of below ~1017/cm3 was extracted from the absorption spectrum and Hall measurement. The densities of micropipes and inclusions in SiC crystal boules grown using the graphite/Ta foil double layer guide tube were significantly decreased. Finally we improved crystal quality through the introduction of new crucible design.

Abstract: SiC crystal boules with different shapes were prepared using sublimation physical vapor transport technique (PVT) and then their crystal quality was systematically investigated. The temperature distribution in the growth system and the crystal shape were controlled by modification of crucible and insulation felt design, which was successfully simulated using “Virtual Reactor” for flat structure design and concave structure design. The SiC polytype proved to be the n-type 6H-SiC from the typical absorption spectrum of SiC crystal. The defect density of SiC crystal boules with concave structure was slightly lower than that of flat structure and the crystal quality of SiC crystal boules with both flat structure and concave structure was significantly improved as the SiC crystal grows during the PVT methods.