Comparative study of two atomic layer etching processes for GaN

Atomic layer etching (ALE) of Ga-polar GaN (0001) using a standard inductively coupled plasma-reactive ion etching system is achieved in this work. The sequential process is using Cl-2 to modify the surface in the adsorption step. For the activation step, the authors compare two rare gas plasmas, namely, Ar and Kr, and show a much larger and well-defined ALE window for the latter. The ALE of GaN is demonstrated by etching mesa structures masked with a photoresist. A constant etching rate per cycle of two monolayers is obtained. The experimental conditions of this self-limited process are found by changing both the adsorption and activation times, together with the source power. This provides an atomic-scale process for nanofabrication, with significant improvements to the GaN surface.