Atom-Scale Dynamics in Surface-Catalyzed Nitrogen Incorporation in Epitaxial Growth of Gallium Nitride

GaN is a principal material in optoelectronics and now emerging as a key material in power electronics [1]. One of the challenges to the device fabrication is the formation of higher quality thin films of GaN, that is not yet achieved to date. We here report density-functional total-energy electronic-structure calculations [2] and Car-Parrinello Molecular Dynamics simulations [3] that clarify atom-scale mechanisms of N incorporation in GaN bonding network during Metal Organic Vapor Phase Epitaxy (MOVPE). The results obtained for the first time in this work include (i) that Ga atoms on the growing surface are extremely mobile at the growth temperature, forming a liquid-like phase, and (ii) that ammonia NH₃ and its related species NH_x intervene into the weak Ga-Ga bond on the growing surface spontaneously or with surprisingly small energy barriers. This finding leads to a conclusion that the epitaxial growth is a reaction enhanced by the existence of weak surface Ga-Ga bonds. Computations have been performed with our own real-space code highly tuned and scalable on for massively parallel HPC architectures.
[1] H. Amano et al., Rev. Mod. Phys. 87, 1133 (2015).
[2] J.-I. Iwata et al., J. Comput. Phys. 229, 2339 (2010).
[3] R. Car and M. Parrinello, Phys. Rev. Lett. 55, 2471 (1985)