Determination of lattice polarity for growth of GaN bulk single crystals and epitaxial layers

Abstract

The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial-on-sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the 〈1–100〉 projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single-crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga-terminated, lattice planes, whereas the rough facets correspond to the (0001̄), N-terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga-terminated orientation.