Spontaneous inversion of in-plane polarity of a-oriented GaN domains laterally overgrown on patterned r-plane sapphire substrates

Spontaneously regulated in-plane polarity inversion of a-oriented GaN domains has been demonstrated for the first time. Crystallographic analysis revealed that each domain grown on circular-hole-patterned r-plane sapphire substrates has basal faces with oppositely oriented in-plane polarity. The inverted orientation of in-plane polarity on the opposite basal faces is not due to merging between in-plane polarity-inverted domains nucleated on the patterned r-plane sapphire substrate, but it was found to be due to spontaneous formation of an inversion domain boundary on the growth fronts of existing domains. This result provides new insights into controlling the in-plane polarity of a-oriented GaN, because the nucleation of in-plane polarity-inverted domains of a-oriented GaN on r-plane sapphire is symmetrically not allowed.