High-resolution imaging of 1:1 [0 0 0 1] ordered a-plane Al0.3Ga0.7N

We report the observation of ordering in Al0.3Ga0.7N as part of an epitaxial lateral overgrowth (ELO) of GaN carried out using (1 1 2¯ 2) GaN templates grown by metal-organic chemical vapor deposition on m-plane sapphire. Transmission electron microscopy showed that the crystalline quality of the ELO GaN was greatly improved when the ELO SiO2 mask was patterned along the [1 1 2¯ 0]sapphire direction. The ELO GaN wings had an inclined columnar shape with smooth (0 0 0 1) and (1 1 2¯ 0) facets. Layers of 1:1 [0 0 0 1] ordered a-plane Al0.3Ga0.7N were observed on the a-plane GaN facets by high-resolution transmission electron microscopy and high-angle annular-dark-field scanning transmission electron microscopy. However, no ordering was observed for c-plane Al0.3Ga0.7N layers grown at the same time on the c-plane GaN facets.