Evolution of Crystal Growth
Homoepitaxial growth on on-axis m-plane GaN yields pyramid features. Pyramids are generated by spiral growth out of pre-existing threading dislocations from the bulk substrate. These AFM images show the evolution of the growth from thin films (~25 nm) to thick layers (~2 Âµm). Thin layers show individual pyramids in a field of meandering steps. The step direction and terrace widths on the pyramids are discernible. As we grow thicker films, the pyramids grow in size and number, and the step orientations are maintained. Thick films are completely covered in overlapping pyramid growth. The step directions visible on the pyramids suggest natural growth directions for the crystal, which we can access by miscutting the substrate a few degrees. Miscut substrates have demonstrated smooth films in the past, and new miscuts suggested by this work may also provide other desirable properties for GaN optoelectronic devices, including longer wavelength emission and lower impurity incorporation.