In-situ decomposition and etching of AlN and GaN in the presence of HCl

The etch rates of gaseous HCl on AlN and GaN in H2 ambient in a MOVPE reactor have been studied. For AlN, etching by HCl in H2 and N2 is compared. When etching GaN in hydrogen by HCl, a dependency of etch rate on temperature was found and the activation energy was determined. We propose a two-step reaction in which the first step, the decomposition of GaN, is the limiting one. The second step consists of a reaction of Ga with HCl to form volatile GaCl. We noticed that the decomposition step is enhanced with increased hydrogen partial pressure. Further, we observed that a coverage of the surface with Ga enhances the decomposition rate. By using a pulsed supply of HCl into the reactor a Ga-rich surface was maintained and the etch rate enhanced up to a temperature of 830 °C.