Plasma-assisted molecular beam epitaxy of NiO on GaN(00.1)

TL;DR

This study investigates the epitaxial growth of NiO on GaN(00.1) substrates using plasma-assisted molecular beam epitaxy across various temperatures, revealing optimal growth conditions and detailed structural and morphological characteristics.

Contribution

It provides new insights into the epitaxial growth mechanisms, domain structures, and temperature-dependent properties of NiO on GaN(00.1) using advanced characterization techniques.

Findings

Epitaxial NiO(111) with two rotational domains was achieved.

Growth temperature influences domain size and surface diffusion length.

High temperature growth leads to substrate decomposition and increased surface roughness.

Abstract

The growth of NiO on GaN(00.1) substrates by plasma-assisted molecular beam epitaxy under oxygen rich conditions was investigated at growth temperatures between 100 $^{\circ}$C and 850 $^{\circ}$C. Epitaxial growth of NiO(111) with two rotational domains, with epitaxial relation $\normalsize{}\mathrm{\mathrm{\mathrm{NiO}(1\bar{\mathrm{{1}}}0)}\:||\:\mathrm{\mathrm{GaN}(11.0)}}$ and $\mathrm{\mathrm{\mathrm{NiO}\mathrm{(10\bar{\mathrm{{1}}})}\:||\:\mathrm{GaN(11.0)}}}$, was observed by X-ray diffraction (XRD) and confirmed by in-situ reflection high-energy electron diffraction as well as transmission electron microscopy (TEM) and electron backscatter diffraction. With respect to the high lattice mismatch of 8.1 % and a measured low residual tensile layer strain, growth by lattice matching epitaxy or domain matching epitaxy is discussed. The morphology measured by atomic force microscopy showed a grainy surface, probably arising from the growth by the columnar rotational domains visible in TEM micrographs. The domain sizes measured by AFM and TEM increase with the growth temperature, indicating an increasing surface diffusion length. Growth at 850 $^{\circ}$C, however, involved local decomposition of the GaN substrate that lead to an interfacial $\mathrm{\beta}$-Ga$\mathrm{_{2}}$O$\mathrm{_{3}}$($\bar{\mathrm{{2}}}$01) layer and a high NiO surface roughness. Raman mesurements of the quasi-forbidden one-phonon peak indicate increasing layer quality (decreasing defect density) with increasing growth temperature. The results above suggest optimum growth temperatures around 700 $^{\circ}$C for high layer and interface quality.