We succeeded in growing a GaN single crystal substrate with diameter of about two inches using the Na flux method. Our success is due to the development of a new apparatus for growing large GaN single crystals. The crystal grown in this study has a low dislocation density of 2:3 Â 10 5 cm À2 . The secondary ion mass spectrometry (SIMS) technique demonstrates that the Na element is difficult to be taken in the crystal in both the ''þ'' and ''À'' c directions, resulting in a Na concentration of 4:2 Â 10 14 cm À3 in the crystal. Our success in growing a two-inch GaN substrate with a low impurity content and low dislocation density should pave the way for the Na flux method to become a practical application.

The behavior of dislocations of GaN single crystals grown using the liquid phase epitaxy (LPE) technique in a Na flux was investigated using a transmission electron microscope (TEM). Almost all dislocations are concentrated around the interface between LPE-GaN and metal organic chemical vapor deposition (MOCVD)-GaN, which was used as a homoepitaxial substrate. It was revealed that the reduction of dislocation is due to an unusual phenomenon in which many (1011) facets are formed in the initial LPE growth period, followed by the development of the GaN(0001) face with further dislocation reduction. On the basis of our TEM observations and an investigation of the surface morphology at each growth stage, we propose a dislocation reduction mechanism during LPE growth.

We succeeded in growing a GaN single crystal substrate with diameter of about two inches using the Na flux method. Our success is due to the development of a new apparatus for growing large GaN single crystals. The crystal grown in this study has a low dislocation density of 2.3×105 (cm-2), The secondary ion mass spectrometry (SIMS) technique demonstrates that the Na element is difficult to be taken in the crystal in both the + and – c directions, resulting in a Na concentration of 4.2 × 1014 (cm-3) in the crystal. Our success in growing a two-inch GaN substrate with a low impurity content and low dislocation density should pave the way for the Na flux method to become a practical application.