Direct van der Waals epitaxy of stress-free GaN films on PECVD grown graphene

Abstract

Residual stress is generated in GaN epitaxial layers due to the mismatch during GaN epitaxy on sapphire using the traditional method. Therefore, the use of graphene to reduce residual stress and dislocation densities in GaN epitaxy has become an important research direction. However, growing a stress-free GaN film on graphene substrate remains challenge. In this work, we directly grew graphene on sapphire via plasma enhanced chemical vapor deposition (PECVD) to obtain an epitaxial graphene with characteristic orientation, and ultra-low stress GaN films can then be obtained through metal organic chemical vapor deposition (MOCVD) assisted with the sputtering AlN buffer layer. Through this method, we successfully obtained continuous and flat GaN films with ultra-low biaxial compressive stress (0.023 GPa) without the complicated stress engineering during epitaxial growth. First principle calculation was employed to confirm that the characteristic orientation of epitaxial graphene is crucial to release the stress in GaN. The obtained GaN films can also be easily transferred because of small van der Waals force on graphene. The transferred GaN heterojunction was directly fabricated into a metal-insulator-semiconductor (MIS) device from which typical electrical properties can be obtained. Our work reveals the stress-releasing mechanism and excellent stress-releasing effect of graphene and provides a new epitaxial strategy to guide crystallographic epitaxy.