Direct observation of hillocks on pendeo-epitaxial GaN films and stabilization of GaN seed layers for hillock-free surface

Hillocks formed on pendeo-epitaxial GaN (PE-GaN) films grown by metalorganic chemical vapor deposition were observed by scanning electron microscopy, atomic force microscopy and high-resolution transmission electron microscopy. In order to suppress hillock formation on PE-GaN films, a two-step growth technique was employed. In the first-step growth, whose growth temperature and V/III ratio were relatively low, it was necessary to suppress hillock formation on the surface, and reduce the crystallographic tilt in the wing regions of PE-GaN films. In the second-step growth, whose growth temperature and V/III ratio were relatively high, complete coalescence without tilt in the wing regions was achieved by a high lateral growth rate.