Structural recovery of ion implanted ZnO nanowires

TL;DR

This study investigates how nitrogen ion implantation and annealing affect the structural and optical properties of ZnO nanowires, revealing enhanced defect recovery compared to bulk material but with optical deterioration likely due to surface effects.

Contribution

It provides a direct comparison of defect recovery mechanisms in ZnO nanowires versus bulk material using TEM and cathodoluminescence.

Findings

Defect recovery is more effective in nanowires due to surface proximity.

Optical emission deteriorates after implantation and annealing.

Surface effects influence exciton dissociation and optical properties.

Abstract

Ion implantation is an interesting method to dope semiconducting materials such as zinc oxide provided that the implantation-induced defects can be subsequently removed. Nitrogen implantation followed by anneals under O2 were carried out on zinc oxide nanowires in the same conditions as in a previous study on bulk ZnO [J. Appl.Phys. 109, 023513 (2011)], allowing a direct comparison of the defect recovery mechanisms. Transmission electron microscopy and cathodoluminescence were carried out to assess the effects of nitrogen implantation and of subsequent anneals on the structural and optical properties of ZnO nanowires. Defect recovery is shown to be more effective in nanowires compared with bulk material due to the proximity of free surfaces. Nevertheless, the optical emission of implanted and annealed nanowires deteriorated compared to as-grown nanowires, as also observed for unimplanted and annealed nanowires. This is tentatively attributed to the dissociation of excitons in the space charge region induced by O2 adsorption on the nanowire surface.