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arXiv · 2501.00561

Characterization of Chromium Impurities in $β$-Ga$_2$O$_3$

Mark E. Turiansky·Sai Mu·Lukas Razinkovas·Kamyar Parto·Sahil D. Patel·Sean Doan·Ganesh Pokharel·Steven J. Gomez Alvarado·Stephen D. Wilson·Galan Moody·Chris G. Van de Walle
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Abstract

Chromium is a common transition-metal impurity that is easily incorporated during crystal growth. It is perhaps best known for giving rise to the 694.3 nm (1.786 eV) emission in Cr-doped Al$_2$O$_3$, exploited in ruby lasers. Chromium has also been found in monoclinic gallium oxide, a wide-bandgap semiconductor being pursued for power electronics. In this work, we thoroughly characterize the behavior of Cr in Ga$_2$O$_3$ through theoretical and experimental techniques. $β$-Ga$_2$O$_3$ samples are grown with the floating zone method and show evidence of a sharp photoluminescence signal, reminiscent of ruby. We calculate the energetics of formation of Cr from first principles, demonstrating that Cr preferentially incorporates as a neutral impurity on the octahedral site. Cr possesses a quartet ground-state spin and has an internal transition with a zero-phonon line near 1.8 eV. By comparing the calculated and experimentally measured luminescence lineshape function, we elucidate the role of coupling to phonons and uncover features beyond the Franck-Condon approximation. The combination of strong emission with a small Huang-Rhys factor of 0.05 and a technologically relevant host material render Cr in Ga$_2$O$_3$ attractive as a quantum defect.

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Mark E. Turiansky, Sai Mu, Lukas Razinkovas, Kamyar Parto, Sahil D. Patel, Sean Doan, Ganesh Pokharel, Steven J. Gomez Alvarado, Stephen D. Wilson, Galan Moody, Chris G. Van de Walle. 2024-12-31. Characterization of Chromium Impurities in $β$-Ga$_2$O$_3$. https://doi.org/10.1063/5.0255859

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