Vibrational and electron-phonon coupling properties of \b{eta}-Ga2O3 from first-principles calculations: Impact on the mobility and breakdown field

Abstract

The wide band gap semiconductor \b{eta}-Ga2O3 shows promise for applications in high-power and high-temperature electronics. The phonons of \b{eta}-Ga2O3 play a crucial role in determining its important material characteristics for these applications such as its thermal transport, carrier mobility, and breakdown voltage. In this work, we apply predictive calculations based on density functional theory and density functional perturbation theory to understand the vibrational properties, phonon-phonon interactions, and electron-phonon coupling of \b{eta}-Ga2O3. We calculate the directionally dependent phonon dispersion, including the effects of LO-TO splitting and isotope substitution, and quantify the frequencies of the infrared and Raman-active modes, the sound velocities, and the heat capacity of the material. Our calculated optical-mode Gr\"uneisen parameters reflect the anharmonicity of the monoclinic crystal structure of \b{eta}-Ga2O3 and help explain its low thermal conductivity. We also evaluate the electron-phonon coupling matrix elements for the lowest conduction band to determine the phonon mode that limits the mobility at room temperature, which we identified as a polar-optical mode with a phonon energy of 29 meV. We further apply these matrix elements to estimate the breakdown field of \b{eta}-Ga2O3. Our theoretical characterization of the vibrational properties of \b{eta}-Ga2O3 highlights its viability for high-power electronic applications and provides a path for experimental development of materials for improved performance in devices.