Improvement of surface morphology of nitrogen-polar GaN by introducing indium surfactant during MOVPE growth

Indium was introduced as a surfactant during metalorganic vapor phase epitaxial growth of nitrogen-polar GaN on c-plane sapphire tilted from 0.2 to 1.0° toward m-axis. For each sample with different tilted angle, the surfactant effect was confirmed from a scanning electron microscope and an atomic force microscope observations. In particular, for the tilted angle of 0.2°, all the hillocks, which usually exist on the nitrogen-polar GaN films on sapphire substrates with low tilted angles, disappeared. The microscopic terrace width was enlarged, and the surface roughness became small irrespective of the tilted angle, however, for the samples with higher tilted angles, the occurrence of the giant step bunching was rather enhanced. Therefore, it was confirmed that indium introduced during the nitrogen-polar GaN growth surely plays a role as a surfactant.