We proposed a nitride semiconductor transverse quasi-phase-matched wavelength conversion device with a polarity inverted structure along the vertical direction formed by surface activated bonding and etching processes. Inductively coupled plasma etching of a GaN layer with maintaining a root-mean square roughness of less than 2 nm in a 100 µm square area was achieved even after deep etching of 1 µm using Cl2/Ar mixture gas and optimizing the antenna and bias powers. This smooth etching enabled surface activated bonding of the ultrathin GaN layer with designed thickness. The fabrication process of the GaN polarity inverted channel waveguide was established.

We have proposed highly efficient microcavity second harmonic generation devices. In this work, we designed and fabricated an a-plane GaN vertical monolithic microcavity second harmonic generation device pumped with a femtosecond laser and obtained normalized wavelength conversion efficiency of 0.15% W−1. The efficiency was comparable to the theoretical estimations taking into account time evolution of fundamental wave intensity in the microcavity, second harmonic generation and even sum frequency generation. This result indicates the possibility of realizing ultra-compact and ultra-efficient devices pumped with long-pulsed or continuous wave lasers, in which the effect of resonance enhancement is even more pronounced.