Strain and stress relationships for optical phonon modes in monoclinic crystals with β-Ga₂O₃ as an example

Authors

Rafal Korlacki, University of Nebraska-LincolnFollow
Megan Stokey, University of Nebraska-LincolnFollow
A. Mock, NRC Research Associateship Programs
Sean Knight, University of Nebraska-LincolnFollow
A. Papamichail, Terahertz Materials Analysis Center and Competence Center for III-Nitride Technology C3NiT–Janzén
V. Darakchieva, Linköping University
Mathias Schubert, University of Nebraska - Lincoln, Linköping University, Leibniz Institute for Polymer ResearchFollow

Date of this Version

11-12-2020

Citation

PHYSICAL REVIEW B 102, 180101(R) (2020). DOI: 10.1103/PhysRevB.102.180101

Comments

Used by permission.

Abstract

Strain-stress relationships for physical properties are of interest for heteroepitaxial material systems, where strain and stress are inherent due to thermal expansion and lattice mismatch. We report linear perturbation theory strain and stress relationships for optical phonon modes in monoclinic crystals for strain and stress situations which maintain the monoclinic symmetry of the crystal. By using symmetry group analysis and phonon frequencies obtained under various deformation scenarios from density-functional perturbation theory calculations on β-Ga₂O₃, we obtain four strain and four stress potential parameters for each phonon mode. We demonstrate that these parameters are sufficient to describe the frequency shift of the modes regardless of the stress or strain pattern which maintain the monoclinic symmetry of the crystal. The deformation potentials can be used together with experimentally determined phonon frequency parameters from Raman or infrared spectroscopy to evaluate the state of strain or stress of β-Ga₂O₃, for example, in epitaxial heterostructures.