Optical, electrical, and mass spectrometry experiments were carried out on solution grown GaN crystals to detect and identify the impurities incorporated in faces of different polarity at different growth condition. Selective etching, photoluminescence and cathodoluminescence imaging indicate that Mg acceptors incorporate preferentially in GaN nitrogen polar face. Larger incorporation of Mg was observed on crystals grown at lower temperatures. Capacitance-voltage measurements verified p-type conductivity due to an excess of Mg acceptors on N-polar face of the GaN crystals. These results suggest that epitaxial layers deposited from liquid phase may be the best approach to produce p-type conducting layers with high hole concentration and low defect density. Published by Elsevier B.V.