First-principles surface energies for monoclinic Ga2O3 and Al2O3 and consequences for cracking of (AlxGa1−x)2O3

Sai Mu,Hartwin Peelaers,Chris G Van De Walle,Mengen Wang

doi:10.1063/5.0019915

Sai Mu, Hartwin Peelaers + Show 2 more

Open Access

https://doi.org/10.1063/5.0019915

Copy DOI

Abstract

Crack formation limits the growth of (AlxGa1−x)2O3 epitaxial films on Ga2O3 substrates. We employ first-principles calculations to determine the brittle fracture toughness of such films for three growth orientations of the monoclinic structure: [100], [010], and [001]. Surface energies and elastic constants are computed for the end compounds—monoclinic Ga2O3 and Al2O3—and used to interpolate to (AlxGa1−x)2O3 alloys. The appropriate crack plane for each orientation is determined, and the corresponding critical thicknesses are calculated based on Griffith’s theory, which relies on the balance between elastic energy and surface energy. We obtain lower bounds for the critical thickness, which compare well with available experiments. We also perform an in-depth analysis of surface energies for both relaxed and unrelaxed surfaces, providing important insights into the factors that determine the relative stability of different surfaces. Our study provides physical insights into surface stability, crack planes, and the different degrees of crack formation in (AlxGa1−x)2O3 films for different growth orientations.

Highlights

Due to its large bandgap (4.76 eV–5.04 eV),1–4 monoclinic β-Ga2O3 provides a large critical electric field strength in field effect transistors (FETs).5,6 Despite being a wide bandgap material, Ga2O3 can be n-type doped.5,7 β-Ga2O3 constitutes a promising platform for applications in high-power electronic devices.Alloying can be used to tune device performance through bandgap engineering
We study the critical thickness for (AlxGa1−x)2O3 films grown on β-Ga2O3 substrates along [100], [010], and [001] directions; among these, the [010] orientation is most commonly used in growth
Critical thickness of (Alx Ga1−x )2O3 films on Ga2O3 We have presented all the information necessary to calculate the brittle fracture toughness and the elastic energy for (AlxGa1−x)2O3 films grown on a Ga2O3 substrate

Summary

Introduction

Due to its large bandgap (4.76 eV–5.04 eV), monoclinic β-Ga2O3 provides a large critical electric field strength in field effect transistors (FETs). Despite being a wide bandgap material, Ga2O3 can be n-type doped. β-Ga2O3 constitutes a promising platform for applications in high-power electronic devices.Alloying can be used to tune device performance through bandgap engineering. Due to its large bandgap (4.76 eV–5.04 eV), monoclinic β-Ga2O3 provides a large critical electric field strength in field effect transistors (FETs).. Alloys with Al have increased bandgaps and enable carrier confinement in heterojunction FETs.. For (AlxGa1−x)2O3 epilayers pseudomorphically grown on β-Ga2O3 substrates with the same crystallographic orientation as the substrate, tensile stress in (AlxGa1−x)2O3 is expected due to the lattice mismatch.. As the elastic energy in the growing film increases, it can lead to the formation of misfit dislocations, surface roughness, V-shaped defects, or cracks, leading to a critical thickness where the strain can no longer be accommodated elastically. For the growth of β-(AlxGa1−x)2O3 films on Ga2O3 substrates, cracks have been found to be the major limitation.. Understanding the mechanism of crack formation is essential for growing the high-quality films required for devices For the growth of β-(AlxGa1−x)2O3 films on Ga2O3 substrates, cracks have been found to be the major limitation. Understanding the mechanism of crack formation is essential for growing the high-quality films required for devices

Methods

Results

Conclusion