Anisotropy, phonon modes, and free charge carrier parameters in monoclinic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>β</mml:mi></mml:math>-gallium oxide single crystals

There is growing interest in low-symmetry metal oxides because of their potential use in high-power electronics capable to sustain very high voltages. Very little is known about their fundamental physical properties, such as transverse and longitudinal optical phonon modes, dielectric constants, and how free charge carriers couple with lattice vibrations. This lack of information is partially due to the complexity by which these properties intertwine due to the low symmetry crystal systems. Here, the authors describe a general pathway to the analysis of long-wavelength experiments for monoclinic and triclinic crystal systems, and they report for the first time a complete set of phonon modes for the monoclinic phase of gallium oxide. These parameters may arrive just in time to support computational optimization of charge and heat transport for device designs. The concept for analysis of long wavelength properties in monoclinic and triclinic crystal systems can help access a widely uncharted field in condensed matter physics.