Enabling the growth of thick, relaxed AlGaN films on bulk GaN substrates

Epitaxial growth of thick, relaxed, homogeneous, and crack-free AlGaN films was demonstrated on single-crystalline GaN substrates. A maskless heteroepitaxial facet-controlled epitaxial lateral overgrowth (FACELO) scheme was developed to relax the lattice mismatch-induced tensile stress via the generation and glide of misfit dislocations at the pyramidal heterointerfaces. Up to 10 μm-thick AlGaN films were demonstrated, which was more than three orders of magnitude beyond the critical thickness for cracking. The expected relaxation mechanism was confirmed by the observation of misfit dislocations at the heterointerfaces via transmission electron microscopy. The developed growth scheme is amenable to the growth of thick, homogeneous, relaxed AlGaN films of any composition on native substrates.