Polycrystalline films were grown onto silica-glass substrates by metal-organic chemical vapor deposition. An n-type conductivity in all of the undoped films was observed, and background impurities such as Si and C were detected. Deep-level emissions at around 2.2eV were attributed to Ga vacancies and C impurity complexes at the grain boundaries.

Effect of Native Defects on Electrical and Optical Properties of Undoped Polycrystalline GaN. S.E.Park, W.S.Han, H.G.Lee, B.O: Journal of Crystal Growth, 2003, 253[1-4], 107-11