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.