AbstractThe difference in surface energy between the Ga‐polar orientation and the N‐polar orientation of GaN translates into a completely different behavior for the incorporation of intentional and unintentional impurities. Oxygen is found to be an impurity with higher concentration in N‐polar films than in Ga‐polar films and is the cause for the high carrier concentration observed in N‐polar films. We fabricated a lateral p/n junction in GaN by the simultaneous growth of p‐ and n‐type regions, utilizing the doping selectivity of the two different polar domains, which resulted in an n‐type carrier concentration of 1.7x1019 cm–3 with an electron hall mobility of 99 cm2/Vs in the N‐polar domains, and a p‐type carrier concentration of 1.1x1017 cm–3 with a hole hall mobility of 12 cm2/Vs in the Ga‐polar domains. These junctions showed the characteristics that define a p/n junction: current rectification, electroluminescence, and photo‐effect. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)