Damage generation and removal in the Ga+ focused ion beam micromachining of GaN for photonic applications

We have investigated focused ion beam (FIB) micromachining of GaN films with the goal of fabricating distributed Bragg reflection air/GaN gratings for short cavity lasers. The FIB micromachining process creates damage in the GaN film. To reduce the damage evidenced in the GaN photoluminescence (PL) spectrum, we utilized both furnace annealing for 1 h and rapid thermal annealing (RTA) from 10 to 50 s at 1050 °C. Pulsed nitrogen and He–Cd lasers have been utilized as excitation sources to study differences in the PL spectra from the FIB-milled distributed Bragg reflector (DBR) gratings and the nonmilled GaN film. Surface roughness does not change with increasing annealing time of RTA. The threshold pumping condition has been investigated to compare the DBR grating area with as grown GaN film. We found that the threshold pumping intensity for these two conditions are almost the same, i.e., FIB micromachining followed by thermal anneal would not degrade the PL spectrum performance of GaN film.