Chemical Etching of GaN in KOH Solution: Role of Surface Polarity and Prior Photoetching

Surface polarity plays a significant role in chemical etching of GaN in KOH solution, a process that is important for quality control and device fabrication. In this work, basic chemical mechanisms are proposed to explain the role of surface orientation in the chemical etching of the semiconductor. In addition, it is shown how prior photoetching of inert surfaces [the polar (0001), semipolar (101̅1̅), and nonpolar (11̅00) interfaces] enables chemical etching. Photoetching gives rise to the formation of nanocolumns on dislocations and to protrusions on nanoscale inhomogeneities. Subsequent etching in KOH solution leads to the development of distinctive features that depend on the crystal orientation of the surface and the presence of the inhomogeneities. The morphology of the photoetched surfaces was revealed by scanning electron microscopy, while X-ray photoelectron spectroscopy measurements were used to investigate the surface chemistry of these processes.