Evidence for Ga clusters in β-Ga2O3 from Raman spectroscopy and density functional theory

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.

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Publication Details

Journal
Journal of Applied Physics
Published
2025-10-03
DOI
https://doi.org/10.1063/5.0292434
Primary Topic
Ga2O3 and related materials
Type
article
Field-Weighted Citation Impact
0.00

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Evidence for Ga clusters in β-Ga2O3 from Raman spectroscopy and density functional theory

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Evidence for Ga clusters in β-Ga2O3 from Raman spectroscopy and density functional theory

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article en

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.

Journal of Applied PhysicsVol. 138(13)
Lawrence Livermore National Laboratory (US), University of California, Santa Barbara (US), Washington State University (US)
U.S. Department of Energy, University of California, Santa Barbara, Multidisciplinary University Research Initiative, Basic Energy Sciences, Laboratory Directed Research and Development, Air Force Office of Scientific Research, Lawrence Livermore National Laboratory
Openalex Percentile: Top 81%
Ga2O3 and related materials
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