Polarity results in different etch pit shapes of screw and edge dislocations in GaN epilayers

Through a comparative study of the scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) results, polarity is found to play an important role in the GaN wet etching process. For the pure screw dislocation it is easy to be etched along the steps that the dislocation terminates. Consequently a small Ga-polar plane is formed to prevent further vertical etching, which results in an etch pit of inverted truncated hexagonal pyramid. However, for the pure edge dislocation it is easy to be etched along the dislocation line, inducing an etch pit of inverted pyramid.