Characterization of Polarity of Wurtzite GaN Film Grown by Molecular Beam Epitaxy Using NH3

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Abstract
Effects of the initial nitridation of a sapphire(0001) substrate by NH3 on the polarity of GaN{0001} film have been investigated by coaxial impact collision ion scattering spectroscopy. The polarity of ammonia-molecular beam epitaxial (MBE) film grown on the substrate nitrided using NH3 is assigned as (0001). The effect of the initial nitridation of the substrate by NH3 is found to be contrary to that by nitrogen plasma, where the GaN film grown on the nitrided substrate shows the polarity of (0001). The polarity of GaN film grown by rf plasma-assisted MBE on the substrate which is nitrided using NH3 is also (0001). These findings suggest the possibility of polarity control of the grown GaN film by choosing the N source for initial nitridation of the substrate.