Epitaxial lateral overgrowth of GaN using hexagonal patterned PECVD and wet transferred graphene masks by MOCVD

Abstract

Epitaxial lateral overgrowth (ELOG) is one of the effective means to improve crystal quality. In this work, gallium nitride (GaN) was grown using a hexagonal patterned graphene as mask via ELOG by metal organic chemical vapor deposition (MOCVD). Two kinds of multi-layer graphene were adopted on GaN/Sapphire compound substrate respectively, one was graphene by plasma enhanced chemical vapor deposition (PECVD), another was wet transferred graphene by chemical vapor deposition (CVD) growth on copper foil. We compared the ELOG behavior of epitaxial GaN and found that the integrity and homogeneity of PECVD graphene made GaN preferentially nucleate and completely cover in the window region. However, because of the large number of defects and winkles introduced during the transfer process, GaN nucleated both in the window region and mask region on the transferred graphene substrate, consequently, epitaxial GaN on transferred graphene was not a ELOG mode. At the same time, we found that both PECVD graphene and transferred graphene was gradually decomposed during the growth process of GaN, but PECVD graphene could still act the mask role. Finally, ELOG GaN on PECVD graphene was obtained and the threading dislocations of GaN on PECVD graphene were greatly reduced and the dislocation distribution was similar to the window pattern. In contrast, the transferred graphene did not act as a mask, and the threading dislocation distribution of epitaxial GaN did not show any regularity.