Thesis (M.Sc.)--Chulalongkorn University, 2010

Cubic GaN (c-GaN) films grown by metalorganic vapor phase epitaxy were investigated using transmission electron microscopy (TEM) to verify effects of growth conditions on the film quality. The c-GaN films used in this study were grown on GaAs (001) and (311) oriented substrates with different growth temperatures of the GaN buffer layers (550-600℃). It is found that all the c-GaN grown films have a cubic structure as a main crystal structure. However, for higher growth temperature, hexagonal phase inclusions found to easily construct along the {111} facets of c-GaN associated with the formation of stacking faults (SFs) starting from the (111) step on the GaAs (001) grown surface. To reduce a generation of hexagonal phase in c-GaN films, growth temperature of a GaN buffer layer is optimized and affected on the formation of SFs in the c-GaN films. The best quality of c-GaN films grown on GaAs (001) substrates with cubic phase purity was achieved by the growth with the optimum growth temperature of GaN films of 900°C and low buffer growth temperature of 575℃. Besides, the c-GaN film on GaAs (311) substrate with identical growth conditions results in the presence of SFs but the hexagonal single crystal is invisible. These results demonstrate that c-GaN on GaAs (311) exhibits a better film quality with lower density of SFs compared to that in c-GaN on GaAs (001). This might be due to a difficulty of a generation of the (111) step on the GaAs (311) grown surface.