Visualization of threading dislocations in an α-Ga2O3 epilayer by HCl gas etching

Threading dislocations in a heteroepitaxial α-Ga2O3 film was visualized as etch pits on the surface. We found that etch pits were formed on a c-plane α-Ga2O3 epilayer by HCl gas etching. The epilayer was prepared by using epitaxial lateral overgrowth technique with a stripe mask pattern. The etch pit density was very high in the window region, and much lower in the laterally grown area on the mask. A line of etch pits was observed at a coalesced boundary. Thus, the etch pit density had a clear correlation with the dislocation density. The correspondence between the etch pits and dislocations was confirmed by cross-sectional bright- and dark-field transmission electron microscopy (TEM). This gas-etching technique can clarify the distribution of dislocations in a wide area, which cannot be explored effectively by TEM.