Characterization of Chromium Impurities in $\beta$-Ga${}_2$O${}_3$

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. $\beta$-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.

References in corpus (5)

• First-principles theory of the luminescence lineshape for the triplet transition in diamond NV centre
• On the origin of red luminescence from iron-doped beta-Ga2O3 bulk crystals
• Rational Design of Efficient Defect-Based Quantum Emitters
• Spin thermometry and spin relaxation of optically detected Cr3+ ions in ruby Al2O3
• Advances in high-pressure laser floating zone growth: the Laser Optical Kristallmacher II

Cited by in corpus (1)

• Approximate Excited-State Potential Energy Surfaces for Defects in Solids