We report on metal organic vapor phase epitaxy (MOVPE) of (0001)InN layers simultaneously grown on a-plane (11 (2) over bar0) and c-plane (0001) sapphire substrates. The substrates were nitridated at temperatures from 500 degrees C to 1050 degrees C prior to the growth of c-plane InN layers. Nitridation determined the polarity, the crystallinity, and the surface morphology of the InN layers. Nitridation temperatures above 800 degrees C lead to N-polar InN layers, while nitridation temperatures from 700 degrees C to 750 degrees C produce mixed-polar InN layers, and nitridation temperatures from 500 degrees C to 650 degrees C produce In-polar InN layers. The roughness and crystallinity of the InN layers are correlated with the changes of polarity. The incorporation of nitrogen into the nitridation layers at different nitridation temperatures was measured. A strong N-Al bond signal after nitridation is correlated with N-polarity layers after overgrowth. (C) 2013 Elsevier B.V. All rights reserved.