Effect of Atomic Layer Etching on n-GaN MOS Capacitors

Abstract

Gallium nitride (GaN) with its high breakdown voltage and low specific on resistance is suitable for high voltage power electronic applications. Common dry etching processes such as reactive ion etching with an inductively coupled plasma (ICP-RIE), however, damage the surface and affect the electrical performance of the fabricated devices. This work aims to investigate the restorative effect of Atomic Layer Etching (ALE) to improve the surface of GaN post dry etching. To this end, Metal-Oxide-Semiconductor capacitors (MOSCAPs) were fabricated on n-doped GaN-on-Si (111) substrates with on wafer splits to study ALE and compare it with ICP-RIE on various rubrics. The sample surfaces were characterized using Atomic Force Microscopy (AFM) and Photoluminescence (PL) measurements while the MOSCAPs were characterized via Capacitance-Voltage (CV) measurements. ALE shows a clear improvement in surface roughness, PL peak intensity and flatband voltage displacement in CV curves when performed on GaN after dry etching. ALE performed on pristine GaN deteriorated the surface, implying that ALE induces damage onto the surface. The ion energy of the sputtered ions in ALE played a key role in the recovery induced onto the surface post dry etching, with lower values causing lower damage, which is preferrable for better end device performance. The number of ALE cycles played no significant role in improving the surface quality. Additionally, a correlation was found between AFM, PL and CV measurements.