Etch-stop process for precisely controlling the vertical cavity length of GaN-based devices

In this study, an etch-stop process was developed using inductively coupled plasma reactive-ion etching for precisely controlling the vertical cavity length of GaN-based devices, such as vertical-cavity surface-emitting lasers (VCSELs) and VCSEL 2D arrays. An AlN layer, which was the etch-stop layer, was added to the epitaxial structure for defining the bottom of a vertical cavity. A uniform vertical cavity length was thus obtained across the entire wafer. Consequently, the flatness of the bottom-end facet was determined from the quality of epitaxial growth rather than the quality of chemical mechanical polishing. The surface morphologies of the wafer in various processing stages were also inspected and compared.