Thesis (Ph.D.)--Chulalongkorn University, 2011

Structural analysis of the cubic-phase GaN (c-GaN) and InN (c-InN) thin films was performed in nano-scale using transmission electron microscopy (TEM) to verify the structural-phase transformation and the structural defect formation, which may be affected by the structural similarities between the cubic (111) and hexagonal (0001) planes with rotating 60. This study found out that the insertion of buffer layer is a successful method to protect the (001) GaAs substrate from thermal decomposition, which introduces the (111) stepped on (001) GaAs surface. This results in a structural-phase transformation from cubic to mixed cubic/hexagonal-phases in the cubic nitride films. Moreover, an anisotropic (111) steps along the [110] and [110] direction of the buffer layer induced anisotropic distribution of defects observed in cross-sectional TEM images taken along the [110] and [110] zone axes. Zone axis dependent type of defects is due to a different atomic structure of surface step on the (001) AlGaAs buffer layer. Cross-sectional TEM images taken along [110] zone axis show a less stacking faults (SFs) but appear a cubic twin with an epitaxial orientation of [114]cubic twin//[110]substrate. Only some treading dislocations were observed on top region of the layer. A present of cubic twin also induced an anti-phase domain boundary in the layer. For the c-InN thin films on MgO (001) substrate with a c-GaN buffer, the In-rich growth condition was found to improve the crystal quality of the c-InN grown layer. Hexagonal phase generation decreased with increasing growth temperature and In flux. However, the structural-phase transformation from cubic to mixed cubic/hexagonal phases in the best quality c-InN films exhibited in a form of planar defects, such as stacking faults and twins generated from the interface between the c-GaN buffer layer and the c-InN film.