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

Vladimir M Kaganer; Oleg V Konovalov; Gabriele Calabrese; David van Treeck; Albert Kwasniewski; Carsten Richter; Sergio Fernández-Garrido; Oliver Brandt

doi:10.1107/S1600576723001486

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

J Appl Crystallogr. 2023 Mar 9;56(Pt 2):439-448. doi: 10.1107/S1600576723001486. eCollection 2023 Apr 1.

Authors

Vladimir M Kaganer¹, Oleg V Konovalov², Gabriele Calabrese^{1

3}, David van Treeck¹, Albert Kwasniewski⁴, Carsten Richter⁴, Sergio Fernández-Garrido^{1

5}, Oliver Brandt¹

Affiliations

¹ Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, 10117 Berlin, Germany.
² ESRF - The European Synchrotron, 71 avenue des Martyrs, 38043 Grenoble, France.
³ Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, via Gobetti 101, 40129 Bologna, Italy.
⁴ Leibniz-Institut für Kristallzüchtung (IKZ), Max-Born-Strasse 2, 12489 Berlin, Germany.
⁵ Institute for Optoelectronic Systems and Microtechnology (ISOM) and Materials Science Department, Universidad Politécnica de Madrid, Avenida Complutense 30, 28040 Madrid, Spain.

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.

Keywords: GISAXS; GaN nanowires; grazing-incidence small-angle X-ray scattering; molecular beam epitaxy; topotaxy.

Grants and funding

Sergio Fernandez-Garrido acknowledges the partial financial support received through the Spanish programme Ramón y Cajal (co-financed by the European Social Fund) under grant No. RYC-2016-19509 from the Ministerio de Ciencia, Innovación y Universidades. He also thanks Universidad Autónoma de Madrid for the transfer to Universidad Politécnica de Madrid of part of the materials and equipment purchased with charge to the RYC-2016-19509 grant.