Influence of patterned graphene mask on nucleation behavior of GaN by MOCVD

We investigated the nucleation behavior of GaN on GaN templates with different periods of graphene masks. It is difficult to ensure the integrity of graphene due to defects such as breakages and wrinkles during the transfer process. Researchers [1]-[2] found that GaN not only nucleates in the window region, but also nucleates at these defects on the graphene mask, and the nucleation mode is different from that on the dielectric mask. Therefore, we plan to enhance the migration of Ga atoms to the window region for nucleation by adjusting the mask period. By comparing the island coverage ratio of GaN on different periods of graphene masks. We found that the island coverage of GaN on graphene masks is sensitive to the change of mask width for samples with windows of 3μm, where the mask-to-periodic width ratio (duty ratio) is less than 0.85. For the samples with windows of 5 gm, the interaction between island coverage ratio and duty ratio was mildly. Both samples with different window widths exhibited a decreasing trend of island coverage ratio with increasing duty ratio, and samples with wider window are more likely to decrease the island nucleation density on graphene masks at low duty ratio. We observed that the GaN strips formed on the window were larger in size and had a distinct semipolar plane {11-2n} in the sample with larger duty ratio. This article focuses on the relationship between the graphene mask period and the nucleation of GaN. These results provide fundamental support for the growth of high quality III-nitrides compounds using graphene masks by epitaxial lateral overgrowth (ELOG).