Molecular beam epitaxy and structural anisotropy of m-plane InN grown on free-standing GaN

This study reports on the growth of high-quality nonpolar m-plane [11¯00] InN films on free-standing m-plane GaN substrates by plasma-assisted molecular beam epitaxy. Optimized growth conditions (In/N ratio ∼1 and T=390–430 °C) yielded very smooth InN films with undulated features elongated along the [112¯0] orientation. This directionality is associated with the underlying defect structure shown by the anisotropy of x-ray rocking curve widths parallel to the [112¯0] (i.e., 0.24°–0.34°) and [0001] (i.e., 1.2°–2.7°) orientations. Williamson–Hall analysis and transmission electron microscopy identified the mosaic tilt and lateral coherence length and their associations with different densities of dislocations and basal-plane stacking faults. Ultimately, very low band gap energies of ∼0.67 eV were measured by optical absorption similar to the best c-plane InN.