Lattice Dynamics of Rutile Germanium Dioxide (r‐GeO ₂ )

ABSTRACT Ultra‐wide bandgap materials are pivotal for next‐generation electronic and optoelectronic devices, yet their widespread adoption is impeded by challenges in bipolar doping. Rutile germanium dioxide (r‐GeO 2 ) is a promising candidate, predicted to enable ambipolar doping and to exhibit high thermal and electronic conductivity. However, critical knowledge gaps remain regarding its lattice dynamics and phonon‐related properties. In this study, we use polarization angle‐resolved Raman spectroscopy on high‐quality, large r‐GeO 2 single crystals to unambiguously determine the energies and relative Raman tensor elements of all first‐order Raman‐active phonons. Our experimental findings are complemented by density functional perturbation theory calculations, which reveal a consistent underbinding of phonon energies across various exchange‐correlation functionals. This highlights a previously unrecognized limitation in the theoretical modeling of r‐GeO 2 . The comprehensive characterization and accurate assignment of phonon modes provide a solid foundation for quantitative simulations of phonon‐assisted processes and pave the way for the design of r‐GeO 2 ‐based devices.