Mapping of damage induced by neutral beam etching on GaN surfaces using scanning internal photoemission microscopy

We applied the method of scanning internal photoemission microscopy (SIPM) to characterize selectively neutral-beam-etched damage, which is much finer than that associated with inductively coupled plasma etching and ion implantation. We used a neutral beam to selectively etch the MOCVD-grown n-GaN surface using Cl₂ gas, and formed Ni Schottky electrodes so that the etching patterns were included in the electrode areas. SIPM measurements were conducted with laser beams whose photon energies were below the bandgap (λ = 405, 517, 660 nm). Photocurrent was detected at each wavelength and a two-dimensional image of photoyield (Y) was obtained; an image of Schottky barrier height (qΦ_B) was also obtained according to the Fowler plot. We clearly observed etching patterns in the Y maps of all the wavelengths. SIPM can sensitively visualize surface damage because etched regions can be compared with unetched regions on the same electrode. In the qΦ_B map, we found that qΦ_B in the etched region increased slightly by 0.1 eV. These results indicate that SIPM is effective for mapping the variation created by etching with high sensitivity.