X-ray scattering study of GaN nanowires grown on Ti/Al$_{2}$O$_{3}$ by molecular beam epitaxy

TL;DR

This study investigates the epitaxial growth and structural properties of GaN nanowires on Ti/Al₂O₃ substrates using X-ray techniques, revealing detailed crystallographic orientations, interfacial reactions, and nanowire size distributions.

Contribution

It provides new insights into the epitaxial growth mechanisms and structural characteristics of GaN nanowires on Ti/Al₂O₃, including detailed modeling of their size and shape distributions.

Findings

GaN nanowires grow epitaxially on TiN layers with low misorientation.

Interfacial reactions produce various Ti-based crystallites with intermediate lattice parameters.

GISAXS modeling determines nanowire size distributions and facet fractions.

Abstract

GaN nanowires (NWs) grown by molecular beam epitaxy on Ti films sputtered on Al$_{2}$O$_{3}$ are studied by X-ray diffraction (XRD) and grazing incidence small-angle X-ray scattering (GISAXS). XRD, performed both in symmetric Bragg reflection and at grazing incidence, reveals Ti, Ti$_{3}$O, Ti$_{3}$Al, and TiO$_x$N$_y$ crystallites with in-plane and out-of-plane lattice parameters intermediate between those of Al$_{2}$O$_{3}$ and GaN. These topotaxial crystallites in Ti film, formed due to interfacial reactions and N exposure, possess fairly little misorientation with respect to Al$_{2}$O$_{3}$. 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 modeled by the Monte Carlo method taking into account the orientational distributions of NWs, a variety of their cross-sectional shapes and sizes, and roughness of their side facets. The cross-sectional size distributions of the NWs and the relative fractions of $(1\bar{1}00)$ and $(11\bar{2}0)$ side facets are determined.