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

Effects of the initial nitridation of a sapphire(0001) substrate by NH 3 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 NH 3 is assigned as (0001). The effect of the initial nitridation of the substrate by NH 3 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 NH 3 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.