Stability of Graphene and Influence of AlN Surface Pits on GaN Remote Heteroepitaxy for Exfoliation

Abstract

Remote epitaxy is a promising technology that has recentlyattractedconsiderable attention, which enables the growth of thin films thatcopy the crystallographic characteristics of the substrate throughtwo-dimensional material interlayers. The grown films can be exfoliatedto form freestanding membranes, although it is often challenging toapply this technique if the substrate materials are prone to damageunder harsh epitaxy conditions. For example, remote epitaxy of GaNthin films on graphene/GaN templates has not been achieved by a standardmetal-organic chemical vapor deposition (MOCVD) method dueto such damages. Here, we report GaN remote heteroepitaxy on graphene/AlNtemplates by MOCVD and investigate the influence of surface pits inAlN on the growth and exfoliation of GaN thin films. We first showthe thermal stability of graphene before GaN growth, based on whichtwo-step growth of GaN on graphene/AlN is developed. The GaN samplesare successfully exfoliated after the first step of the growth at750 degrees C, whereas the exfoliation failed after the second stepat 1050 degrees C. In-depth analysis confirms that the pits in AlN templateslead to the degradation of graphene near the area and thus the alterationof growth modes and the failure of exfoliation. These results exemplifythe importance of chemical and topographic properties of growth templatesfor successful remote epitaxy. It is one of the key factors for III-nitride-basedremote epitaxy, and these results are expected to be of great helpin realizing complete remote epitaxy using only MOCVD.