Molecular beam epitaxy of GaN on 2H–MoS2

Recent interest in the heterogeneous integration of two-dimensional (2D) materials with three-dimensional (3D) semiconductors has resulted in the implementation of direct heteroepitaxial growth via various epitaxy techniques. In this study, we demonstrated the synthesis of wafer-scale direct growth of GaN on MoS2 using plasma-assisted molecular beam epitaxy. Systematic studies were employed to understand the growth diagram of GaN on large area multi-layer MoS2, and various growth parameters such as substrate temperature and Ga to N flux ratio were investigated to study the degradation mechanism of the underlying MoS2 layer. The growth diagram of GaN on MoS2 was proposed based on the studies. The microstructure of GaN (i.e., N-rich and 550 °C) was evaluated by scanning transmission electron microscopy. Phase segregation was found in the N-rich GaN layer. A two-step growth process involving N-rich condition at a lower temperature and Ga-rich condition at a higher growth temperature was attempted to obtain the smooth and high crystalline quality of GaN. While the two-step growth method led to substantial improvement in the film quality, the removal of MoS2 was observed and the degradation of MoS2 substrate was attributed to Ga diffusion through dislocation lines based on energy-dispersive x-ray spectroscopy mapping. This work helps illuminate critical issues in the epitaxial growth of conventional semiconductors on 2D crystals for various device applications.