Evidence for Ga clusters in β-Ga2O3 from Raman spectroscopy and density functional theory
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.
Article Details
Journal Info
Journal of Applied Physics
American Institute of Physics
Authors (11)
Jesse Huso
Klar Scientific 1 , 1615 NE Eastgate Blvd., Unit G, Ste. 3E, Pullman 99163, Washington,
Benjamin Dutton
Washington State University 2 Institute of Materials Research. , Pullman 99164, Washington,
Cassandra Remple
Washington State University 2 Institute of Materials Research. , Pullman 99164, Washington,
Matthew D. McCluskey
School of Mechanical and Materials Engineering, Washington State University 1 , Pullman, Washington 99164,
John S. McCloy
School of Mechanical and Materials Engineering, Washington State University 2 , Pullman, Washington 99164,
Arkka Bhattacharyya
Materials Department, University of California Santa Barbara , Santa Barbara, California 93106,
Sriram Krishnamoorthy
Materials Department, University of California Santa Barbara , Santa Barbara, California 93106,
Steve Rebollo
Materials Department, University of California , Santa Barbara, California 93106,
James S. Speck
Materials Department, University of California Santa Barbara 2 , Santa Barbara, California 93106,
Joel B. Varley
Lawrence Livermore National Laboratory
Lars F. Voss
Lawrence Livermore National Laboratory 4 , Livermore 94551, California,