MBE grown preferentially oriented CdMgO alloy on m- and c-plane sapphire substrates

TL;DR

This study investigates the growth, structure, and optical properties of CdMgO alloys on m- and c-plane sapphire substrates using plasma-assisted molecular beam epitaxy, revealing orientation-dependent crystallography and tunable bandgaps.

Contribution

It demonstrates the preferential crystallographic orientation of CdMgO alloys on different sapphire planes and analyzes how Mg incorporation affects optical properties.

Findings

Cubic rock salt structure confirmed for CdMgO.

Distinct <111> and <110> orientations on c- and m-plane sapphire.

Mg incorporation influences the optical bandgap and bowing parameter.

Abstract

Unlike other II-VI semiconductors, CdO-based transparent oxide has great potential application for the fabrication of many optoelectronic devices. In this work, we study the growth of CdxMg1-xO alloys on m- and on c-plane sapphire substrates in Cd-rich to Mg-rich conditions using the plasma-assisted molecular beam epitaxy method. A structural and morphological study of CdMgO random alloys was carried out using X-ray diffraction and Atomic Force Microscope (AFM) techniques whereas composition analysis was done by Energy-dispersive X-ray (EDX) spectroscopy method. The optical properties of thin films were investigated by UV-Vis spectroscopy at room temperature. X-ray analysis confirmed the presence of cubic rock salt structure with <111> CdMgO crystallographic orientation on c-plane sapphire and <110> CdMgO preferential orientation on m-plane sapphire. The surface roughness was measured by the AFM. From the absorption curve, the optical bandgaps were determined using Tauc relation and it was found that the bandgap of films is influenced by the incorporation of Mg2+ ions into the CdO lattice. Bowing parameter was calculated both for samples on m- and c- sapphires.