Evidence of O‐Polar (0001¯) ZnO Surfaces Induced by In Situ Ga Doping

Abstract

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 (000) 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.