GaN Single Crystalline Domain Growth on Graphene Substrate

Abstract

Graphene is very well known 2D nano-material which have novel physical and chemical properties even in a few layer thick form. Recently, there have been extensive studies on hetero-structures based on these Van-der-Waals 2D crystals like graphene, transition metal dichalcogenide (TMD), boron nitride (BN) and so on. In the case of graphene, this 2D layer can be stable and can be transferred to other target substrate with ease. Therefore, graphene can be a good candidate materials for growing other active materials on it. In this study, we tried to grow GaN micro-domain on graphene substrate using hydride vapor phase epitaxy (HVPE) method. GaN epitaxial behavior can be affected by the condition of graphene substrate and we compared the growth behavior of GaN micro-domain on graphene changing the preparation condition. And, several experimental parameters could be controlled like flow rate of Ga and N source with carrier gas, temperature and time to get the proper morphology of GaN micro-crystals. Despite of lattice mis-match of hexagonal GaN on graphene, we could grow single crystalline GaN micro-domain having the lateral size of a few or lager microns. We characterized these micro-crystalline GaN domains using optical microscopy, secondary electron microscope (SEM), micro-Raman spectroscopy and x-ray diffraction (XRD) which confirmed the crystalline phase of each domain. As a typical Van-der-Waals crystal, pristine non-defective graphene may have lacking dangling bonds leading to very low nucleation density for GaN growth and can be used even as a mask layer. When grown on the transferred graphene, however, we expect to have enough nucleation sites originating from the physical defects like grain boundary, vacancy and ripples of poly-crystalline graphene layer. This experimental finding is very interesting to further studies of graphene applications for hetero-structures of graphene and other complementary active materials because graphene has disadvantage in the applications of switching devices, optical elements and can be a potential candidate to overcome these weak points by utilizing very efficiently active GaN together.[1] Y. Kim et al., Nature, 544, p.340 (2017)[2] V. Kumaresan et al,, Nano Letters, 16, p.4895 (2016)