Phonons in Single‐Domain κ‐Ga ₂ O ₃ Studied by Polarization Angle‐Resolved Raman Scattering

ABSTRACT Gallium oxide (Ga 2 O 3 ) is an ultra‐wide bandgap semiconductor with several polymorphs, among which the orthorhombic κ‐phase is particularly attractive for high‐power electronics, non‐volatile memory, and charge‐tunable devices due to its large spontaneous polarization and potential ferroelectric behavior. However, commonly grown κ‐Ga 2 O 3 thin films contain nanoscale rotational domains, hindering the characterization of intrinsic properties and complicating device integration. In this work, we present the first combined experimental and theoretical Raman spectroscopy study of single‐domain κ‐Ga 2 O 3 thin films grown on orthorhombic ε‐GaFeO 3 substrates. Using polarization‐ and angle‐resolved Raman spectroscopy, we identify over 100 phonon modes, which correlate with 117 modes calculated via density functional perturbation theory. A systematic nomenclature is introduced based on mode symmetry and frequency to aid identification and comparison across future studies. Direct comparison with rotational‐domain samples shows that single‐domain films exhibit pronounced angle‐dependent Raman intensities consistent with theoretical selection rules, features that are obscured in multi‐domain films due to domain averaging. These findings establish polarization angle‐resolved Raman spectroscopy as an effective alternative to XRD and TEM for domain structure analysis and provide a robust framework for further studies of κ‐Ga 2 O 3 in electronic applications.