Oxygen is doped into a gallium nitride crystal by preparing a non-C-plane gallium nitride seed crystal, supplying material gases to the seed crystal, growing a non-C-plane gallium nitride crystal on the seed crystal and allowing oxygen to infiltrate via a non-C-plane surface to the growing crystal. Otherwise, oxygen is doped into the crystal by preparing a C-plane gallium nitride seed crystal or a three-rotationally symmetric plane foreign material seed crystal, supplying material gases to the C-plane seed crystal or the foreign seed crystal, growing a faceted C-plane gallium nitride crystal having facets of non-C-planes on the seed crystal, maintaining the facets on the crystal and allowing oxygen to infiltrate via the non-C-plane facets to the crystal.