Metal-organic chemical vapor deposition of MgGeN2 films on GaN and sapphire

TL;DR

This study demonstrates the synthesis and characterization of MgGeN2 films on GaN and sapphire substrates using metal-organic chemical vapor deposition, revealing their structural, optical, and compositional properties relevant for optoelectronic applications.

Contribution

It introduces a detailed growth process for MgGeN2 films via MOCVD and provides comprehensive characterization data, advancing understanding of this material's properties and potential uses.

Findings

Films are highly crystalline with preferential orientation.

Band gap measured at approximately 4.28 eV.

Surface roughness around 10 nm across samples.

Abstract

MgGeN2 films were synthesized using metal-organic chemical vapor deposition on GaN/c-sapphire templates and c-plane sapphire substrates. Energy-dispersive X-ray spectroscopy was used to estimate the cation composition ratios. To mitigate magnesium evaporation, the films were grown at pyrometer temperature 745 {\deg}C with a wafer rotation speed of 1000 rpm. Growth rates were determined by fitting energy-dispersive X-ray spectroscopy spectra to film thicknesses using NIST DTSA-II software. The thickness estimates determined by this method were consistent with scanning transmission electron microscopy measurements done for selected samples. Scanning electron microscopy images revealed faceted surfaces indicative of a tendency toward three-dimensional growth. X-ray diffraction spectra confirmed that the films were highly crystalline and exhibited preferential orientation in alignment with the substrate. Atomic force microscopy measurements show that film thicknesses are consistent across samples grown on both GaN templates and sapphire substrates, with typical roughnesses around 10 nm. Transmittance spectra of films grown on double-side-polished sapphire substrates yielded band gaps of 4.28 +- 0.06 eV for samples exhibiting close-to-ideal stoichiometry. Comparison of the measured spectra with ab initio calculations are in good agreement both near the band gap and at higher energies where excitation is into higher-lying bands. These findings provide insight into the growth and characterization of MgGeN2, contributing to the development of this material for potential applications in optoelectronics and power electronics.