Laser molecular beam epitaxy of ZnO thin films and heterostructures

TL;DR

This paper details the growth and characterization of high-quality epitaxial ZnO thin films and heterostructures on sapphire substrates using laser molecular beam epitaxy, emphasizing technical advancements and potential spintronic applications.

Contribution

It introduces advanced laser-MBE techniques for ZnO film growth, optimizing parameters for high-quality epitaxial layers and demonstrating multilayer heterostructures suitable for spintronics.

Findings

High structural quality of epitaxial ZnO films achieved

Successful growth of multilayer heterostructures with good in-plane epitaxy

Potential for spin transport experiments demonstrated

Abstract

We report on the growth of epitaxial ZnO thin films and ZnO based heterostructures on sapphire substrates by laser molecular beam epitaxy (MBE). We first discuss some recent developments in laser-MBE such as flexible ultra-violet laser beam optics, infrared laser heating systems or the use of atomic oxygen and nitrogen sources, and describe the technical realization of our advanced laser-MBE system. Then we describe the optimization of the deposition parameters for ZnO films such as laser fluence and substrate temperature and the use of buffer layers. The detailed structural characterization by x-ray analysis and transmission electron microscopy shows that epitaxial ZnO thin films with high structural quality can be achieved, as demonstrated by a small out-of-plane and in-plane mosaic spread as well as the absence of rotational domains. We also demonstrate the heteroepitaxial growth of ZnO based multilayers as a prerequisite for spin transport experiments and the realization of spintronic devices. As an example, we show that TiN/Co/ZnO/Ni/Au multilayer stacks can be grown on (0001)-oriented sapphire with good structural quality of all layers and well defined in-plane epitaxial relations.