Plasma reactive ion etching-induced damage in gallium nitride

Characterization of the reactive ion etching (RIE) damage in GaN has been conducted using I-V characteristics of Schottky structures made on etched GaN samples, photoluminescence and X-ray photoelectron spectroscopy (XPS).; In the first part of this work, we investigated RIE- and Photo-Assisted RIE (PA-RIE)-induced damage in GaN using Schottky structures and a BCl 3/Cl2/N2 gas mixture. Schottky diode IN characteristics following different RF powers and exposure times showed significant changes due to the plasma process. There was evidence of reduced damage due to the presence of light that we explained by a photo-enhanced defect diffusion phenomenon leaving a cleaner near-surface region. In the second part of this work, we were interested in the effect of nitrogen on the etching process, and in the resulting damage. n-GaN samples were etched with RIE in BCl3/Cl 2/Ar and BCl3/Cl2/N2 plasmas. Replacing argon by nitrogen in the plasma chemistry resulted in better etch rates, and in addition reduced etch damage for relatively low values of the plasma power. By treating the samples in a nitrogen plasma following etching, we dramatically reduced surface damage, as determined from Schottky IV characteristic measurements. Further, XPS analysis showed that the N2 post-etch nitrogen decreased the Ga/N ratio. These results suggest that much of the damage induced by RIE plasma etching comes from a nitrogen loss mechanism. Photoluminescence (PL) experiments showed an increased intensity of the donor-acceptor (D-A) peak and a reduced band-edge peak due to damage. That phenomenon is reduced in the case of samples treated with a N2 post-etch plasma, indicating that etching damage of n-GaN enhances a defect level population that participates in the D-A transition. The characterization results lead to the conclusion that a significant part of the etch-induced damage is most likely related to donors created by nitrogen vacancies which result from the N2 loss from the GaN surface during the RIE etching.