Cu 2+ and Cu 3+ Acceptors in β-Ga 2 O 3 Crystals: A Magnetic Resonance and Optical Absorption Study
Electron paramagnetic resonance (EPR) and optical absorption are used to characterize Cu2+ (3d9) and Cu3+ (3d8) ions in Cu-doped β-Ga2O3. These Cu ions are singly ionized acceptors and neutral acceptors, respectively (in semiconductor notation, they are Cu− and Cu0 acceptors). Two distinct Cu2+ EPR spectra are observed in the as-grown crystals. We refer to them as Cu2+(A) and Cu2+(B). Spin-Hamiltonian parameters (a g matrix and a 63,65Cu hyperfine matrix) are obtained from the angular dependence of each spectrum. Additional electron-nuclear double resonance (ENDOR) experiments on Cu2+(A) ions give refined 63Cu and 65Cu hyperfine matrices and provide information about the nuclear electric quadrupole interactions. Our EPR results show that the Cu2+(A) ions occupy octahedral Ga sites with no nearby defect. The Cu2+(B) ions, also at octahedral Ga sites, have an adjacent defect, possibly an OH− ion, an oxygen vacancy, or an H− ion trapped within an oxygen vacancy. Exposing the crystals at room temperature to 275 nm light produces Cu3+ ions and reduces the number of Cu2+(A) and Cu2+(B) ions. The Cu3+ ions have an S = 1 EPR spectrum and are responsible for broad optical absorption bands peaking near 365, 422, 486, 599, and 696 nm. An analysis of loops observed in the Cu3+ EPR angular dependence gives 2.086 for the g value and 22.18, 3.31, and −25.49 GHz for the principal values of D (the fine-structure matrix). Thermal anneal studies above room temperature show that the Cu3+ ions decay and the Cu2+ ions recover between 75 and 375 °C.
Journal of Applied Physics
T. D. Gustafson, N. C. Giles, B. C. Holloway, C. A. Lenyk, J. Jesenovec, J. S. McCloy, M. D. McCluskey, and L. E. Halliburton , "Cu2+ and Cu3+ acceptors in β-Ga2O3 crystals: A magnetic resonance and optical absorption study", Journal of Applied Physics 131, 065702 (2022) https://doi.org/10.1063/5.0080502
© 2022 Author(s). Published under an exclusive license by AIP Publishing.
The "Download" button on this page provides the CHORUS-furnished accepted manuscript (postprint) of the article.
A 12-month embargo was imposed on the accepted manuscript.
The published version of record (VOR) for the article is cited below, and is available by subscription at the link in the citation.