Evidence of O‐Polar (000 1 ¯ ) ZnO Surfaces Induced by In Situ Ga Doping

• Published in: Physica status solidi. PSS-RRL. Rapid research letters 2020-06, Vol.14 (6), p.n/a
• Main Authors: Sallet, Vincent, Sartel, Corinne, Arnold, Christophe, Hassani, Said, Vilar, Christèle, Amiri, Gaelle, Lusson, Alain, Galtier, Pierre, Barjon, Julien, Masenelli-Varlot, Karine, Masenelli, Bruno
• Format: Article
• Language: English
• Subjects: Cathodoluminescence; Condensed Matter; crystal facets; Doping; Electron diffraction; Emission analysis; Flat surfaces; Gallium; Materials Science; Metalorganic chemical vapor deposition; Nanostructure; Nanowires; Organic chemicals; Organic chemistry; Physics; Polarity; Surface properties; Towers; transmission electron microscopy; Trees; Vapor phases; Zinc oxide; ZnO nanowires
• ISSN: 1862-6254; 1862-6270
• DOI: 10.1002/pssr.202000037

Controlling the facet orientation and polarity of semiconductor nanostructures is a major issue for achieving devices requiring specific surface properties. Herein, new facets are created during the growth of ZnO nanowires (NWs) by metal‐organic chemical vapor deposition, as a consequence of the trimethylgallium flow introduced in the gas phase. This in situ Ga‐doping induces original shapes such as “Christmas tree”‐like and “Taipei tower”‐like nanostructures, developed along the C‐axis direction. In particular, lateral facets exhibit polar surfaces normal to this growth direction, which can be seen either as overhangs (for Christmas trees) or as terraces (for Taipei towers). In both cases, convergent beam electron diffraction reveals that those surfaces are O‐polar (0001¯) planes, so that the two kinds of nano‐objects grow with opposite polarities, i.e., Zn‐polar (+C) for Christmas trees and O‐polar (−C) for Taipei towers. By confirming previously published theoretical calculations, this work provides an experimental evidence that Ga doping favors the growth of O‐polar ZnO facets instead of the nonpolar M‐surfaces usually developed for undoped ZnO NWs. Nano‐cathodoluminescence studies emphasize the intense near band edge emission of the nanostructures in the ultraviolet range, demonstrating their high optical quality. In situ Ga doping during the metal‐organic chemical vapor deposition (MOCVD) growth of Au‐catalyzed ZnO nanowires induces the formation of new O‐polar surfaces. Crystal facet engineering is achieved through the modification of surface energies. Nanostructures having opposite polarities are generated: Christmas trees grown along +C (0001) axis exhibit overhangs, whereas Taipei towers along –C (0001¯) axis show terraces.