Ritsumeikan University，Shinichiro Mouri
We have studied to control valley-spin polarization of layered materials such as MoS2 using polarization field (spontaneous polarization, piezo polarization) of semiconductors in the publicly offered research. Van der Waals epitaxy of nitride semiconductors, the crystal growth of thin film on layered materials, is an essential technique to fabricate the quantum well structure used in our study. We have recently proposed the growth procedure named “Metal covered van der Waals epitaxy” to grow thin film of gallium nitride (GaN) on graphene .
Crystal growth of GaN on graphene have been studied intensively all over the world towards applications for optical devices or power devices. However, there is the issue that nano-crystals with random orientation are often grown on a graphene as shown in Fig. a due to the impact of nitrogen radicals or ions on it. Here, we demonstrated that Ga covering of graphene at the initial growth stage and consequent nitride growth under nitrogen plasma rich supply was effective to obtain the GaN thin film. Suppression of plasma impact on graphene could reduce the generation of dangling bonds as nucleation sites of misoriented crystals. This method was more effective on the GaN substrate because of the effects of quasi-homoepitaxy, resulting in the growth of highly c- axis oriented flat film as shown in Fig. b. We consider that our findings could progress the research on quantum well devices composed of layered materials and conventional compound semiconductors. U. Ooe, S. Mouri et al, Jpn. J. Appl. Phys. 58, SC1053 (2019).