Improvement of III-N surfaces after inductively coupled plasma dry etch exposure

In this work, two distinct dry-etch processing issues were observed: build-up of material on mesa sidewalls, and pillar formation on etched surfaces. Material accumulation at the mesa edges is introduced during the mesa etch, and is not removed during subsequent solvent and acid cleans. Conductive Atomic Force Microscopy (C-AFM) scans reveal that the material is more conductive relative than the mesa defined junction, providing a leakage path for current. I-V measurements of GaN p-i-n junction diodes indicate that the as-etched junctions are in fact quite leaky, with turn-on voltages of <1V where a ∼ 3V turn-on is expected. Removal of the excess material by a boiling 0.2M KOH solution significantly reduces the leakage, and yields diode curves with a 3V turn-on. Pillar formation typically occurs when non-volatile etch products micro-mask the surface. Scanning electron micrographs of an n-GaN surface with significant pillar formation, show pillar heights of approximately 100nm. Exposing the surface to a boiling 0.2M KOH solution for 2 minutes removes the pillars and significantly improves the surface morphology.