X-ray scattering study of GaN nanowires grown on Ti/Al₂O₃ by molecular beam epitaxy

Abstract

GaN nanowires (NWs) grown by molecular beam epitaxy on Ti films sputtered on Al2O3 are studied by X-ray diffraction (XRD) and grazing-incidence small-angle X-ray scattering (GISAXS). XRD, performed both in symmetric Bragg reflection mode and at grazing incidence, reveals Ti, TiN, Ti3O, Ti3Al and Ga2O3 crystallites with in-plane and out-of-plane lattice parameters intermediate between those of Al2O3 and GaN. These topotaxial crystallites in the Ti film, formed as a result of interfacial reactions and N exposure, possess little misorientation with respect to Al2O3. As a result, GaN NWs grow on the top TiN layer, possessing a high degree of epitaxial orientation with respect to the substrate. The measured GISAXS intensity distributions are modelled by the Monte Carlo method, taking into account the orientational distributions of NWs, the variety of their cross-sectional shapes and sizes, and the roughness of their side facets. The cross-sectional size distributions of the NWs and the relative fractions of the {1100} and {1120} side facets are determined.

Density control of GaN nanowires at the wafer scale using self-assembled SiN x patches on sputtered TiN(111)

“…Hence, we propose that the unusually large PL linewidth observed here for single GaN nanowires relates to the presence of a thick and disordered native oxide, which builds inhomogeneous strain and/or induces a large potential fluctuation due to a random distribution of ionized states. The presence of a few nanometer thick oxide shell has already been proposed to account for the roundish shape of many GaN nanowires grown on Ti films, which contrasts with the hexagonal shape of most GaN nanowires grown on Si substrates [84]. The oxide is believed to form as a result of massive Ga incorporation in the Ti layer during exposure to the Ga flux [54].…”