Suppression of Surface Defects and Vibrational Coupling in GaN by a Graphene Monolayer

Abstract

The optical transitions and random walking dynamics of the three types of excitons, namely, free, donor-bound, and acceptor-like surface-defect-bound excitons, in both the graphene−GaN hybrid structure and bare GaN are comparatively examined using variable-temperature steady-state photoluminescence and time-resolved photoluminescence. The results reveal that the effective suppression of surface defects may be realized by a graphene capping monolayer, evidenced by the strong reduction of the luminescence signal of the surface-defect-bound excitons and the simultaneous enhancement of the free exciton luminescence. More interestingly, the coupling strengths between all the three kinds of excitons and the longitudinal optical phonons tend to weaken, especially for the surface-defect-bound excitons, which exhibit a reduction of ≈40%. These findings indicate that capping GaN by graphene could be an effective way to passivate harmful surface defects and address the heating problem in GaN-based devices.