New insights into crystallographic relation and lattice dynamics effects in {CdO/MgO} superlattices grown by plasma-assisted molecular beam epitaxy

TL;DR

This study investigates how substrate orientation affects the structural quality and growth dynamics of {CdO/MgO} superlattices grown by plasma-assisted molecular beam epitaxy, revealing orientation-dependent effects on twin formation and layer thickness.

Contribution

It provides new insights into the influence of substrate crystallography on superlattice quality and growth rates, highlighting the role of surface symmetry and orientation.

Findings

No twins observed on r-oriented sapphire substrates.

Growth rate of CdO layers depends on substrate orientation.

c-plane and m-plane substrates produce thicker CdO layers.

Abstract

This article explores the structural properties of molecular beam epitaxy grown {CdO/MgO} superlattices on sapphire substrates of different crystallographic orientations (a-, c-, r-, and m-plane). The investigations involve a comprehensive analysis using X-ray diffraction and Raman spectroscopy. High-resolution X-ray diffraction studies unveil a significant influence of surface symmetry on both the substrates and the epitaxial layers, particularly with respect to the occurrence of twins in the superlattices. Remarkably, no twins are observed on r-oriented sapphire substrates, resulting in improved interface and crystallographic quality. The results of studies demonstrated in this work show that the growth rate of CdO sublayers within {CdO/MgO} superlattices is intricately dependent on the substrate orientation. Notably, the c-plane and m-plane sapphire substrates yielded thicker CdO sublayers, indicating comparable growth rates for these crystallographic orientations. Conversely, the a-plane and r-plane orientations seemed to favor a slower growth rate of CdO sublayers.