【Epitaxy Papers】Evidence for Ga clusters in β-Ga₂O₃ from Raman spectroscopy and density functional theory

      Researchers from the Washington State University have published a dissertation titled "Evidence for Ga clusters in β-Ga₂O₃ from Raman spectroscopy and density functional theory" in Journal of Applied Physics.

Abstract

      Monoclinic gallium oxide (β-Ga₂O₃) single crystals have a Raman mode at ∼250 cm⁻¹ that is strongly correlated with free-electron density. Prior work attributed this peak to an electronic excitation of a shallow donor impurity band. However, heavily n-type thin films grown by metalorganic chemical vapor deposition or molecular beam epitaxy do not have the peak. In the present work, an alternate model is proposed: the 250 cm⁻¹ Raman peak arises from Ga clusters, defined as two or more Ga atoms that form Ga–Ga bonds. Raman mapping reveals variations in the frequency that are consistent with a distribution of cluster sizes. The intensity of the peak decreases as the temperature is raised, attributed to melting of the Ga clusters. First-principles calculations indicate that the 250 cm⁻¹ mode is due to Ga–Ga bond-stretching vibrations. As the Fermi energy is raised, the formation of Ga–Ga dimers becomes energetically favorable, explaining the correlation between n-type conductivity and the appearance of the Raman peak.

DOI：

https://doi.org/10.1063/5.0292434