Influence of excess silicon on polytype selection during metal-mediated epitaxy of GaN nanowires

• Published in: Applied physics letters 2024-07, Vol.125 (4)
• Main Authors: Liu, A., Xi, Z., Li, M., Yang, J. C., Qi, L., Goldman, R. S.
• Format: Article
• Language: English
• Subjects: Crystal structure; Crystallography; Density functional theory; Electron diffraction; Energy dispersive X-ray spectroscopy; Epitaxy; Focused ion beam; Free energy; Gallium nitrides; Heat of formation; Heterostructures; Molecular beam epitaxy; NANOSCIENCE AND NANOTECHNOLOGY; Nanowires; Scanning transmission electron microscopy; Silicon substrates; Transmission electron microscopy; Wurtzite; Zincblende
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0210669

We have examined the origins of polytype selection during metal-mediated molecular-beam epitaxy of GaN nanowires (NWs). High-angle annular dark-field scanning transmission electron microscopy reveals [111]-oriented zinc blende (ZB) NWs and [0001]-oriented wurtzite (WZ) NWs, with SixNy at the interface between individual NWs and the Si (001) substrate. Quantitative energy dispersive x-ray spectroscopy reveals a notably higher Si concentration of 7.0% ± 2.3% in zinc blende (ZB) NWs than 2.3% ± 1.2% in wurtzite (WZ) NWs. Meanwhile, density functional theory calculations show that incorporation of 8 at. % Si on the Ga sublattice inverts the difference in formation energies between WZ and ZB GaN, such that the ZB polytype of GaN is stabilized. This identification of Si and other ZB polytype stabilizers will enable the development of polytype heterostructures in a wide variety of WZ-preferring compounds.