Epitaxial growth of GaN has been investigated by a large number of people. However

few publications relate to the pattern of the formation of pits and hills on the surface of GaN epitaxial layers during the growth process. Some authors have given an explanation based on the growth mechanism of GaAsP. They believe that the formation of pits or hills on the surface of GaN epitaxial layers probably depends on the amount of GaCl in the growing zone. If GaCl in the growing zone is not enough

pits will occur. On the contrary

hills will be caused. We have investigated the effect of conversion rate of HC1 and Ga on the morphology of GaN. Our experimental results are contradictory to the reference as mentioned above. A tentative explanation is given in this paper.