Epitaxy

Engineering

Transmission electron microscopy

Materials science

Layer (electronics)

Telecommunications

Computer science

Coaxial

Physics

Nanotechnology

Optics

Cathodoluminescence

Luminescence

Heterojunction

Optoelectronics

Nanorod

Passivation

Electrical engineering

The Journal of Physical Chemistry C

Vertically aligned, single-crystalline ZnO/MgZnO coaxial nanorod arrays were epitaxially grown on GaN substrates by hydrothermal synthesis combined with pulsed laser deposition. Well-defined core/shell heterostructures with high-quality interfaces and coherent epitaxial relationship were confirmed by Z-contrast scanning transmission electron microscopy and line-scan compositional analyses. It is interesting to note that the MgZnO shell thickness gradually decreases from the tip to the base of the nanorods, due to a shadow effect during the deposition. The nonuniform coating allows us to study the carrier confinement and surface passivation effects on a single nanorod. Spatially resolved cathodoluminescence measurements reveal that the band-edge emission intensity of ZnO cores is variable along their length, and depends strongly on the shell thickness. A model, which involves carrier tunneling, surface trapping, and radiative/nonradiative recombination processes, was developed to understand this phenomenon. However, a high-temperature thermal treatment may lead to the stress relaxation and the formation of interfacial defects, and enhance the interdiffusion of interfacial atoms. These degrade the optical quality of coaxial nanorods.

Heteroepitaxial Growth and Spatially Resolved Cathodoluminescence of ZnO/MgZnO Coaxial Nanorod Arrays