On the origin of red luminescence from iron-doped β-Ga2O3 bulk crystals

Abstract

Currently, Fe doping in the ∼10¹⁸ cm⁻³ range is the most widely available method for producing semi-insulating single crystalline $\beta$ -Ga₂O₃ substrates. Red luminescence features have been reported from multiple types of Ga₂O₃ samples, including Fe-doped $\beta$ -Ga₂O₃, and attributed to Fe or N_O. Herein, however, we demonstrate that the high-intensity red luminescence from Fe-doped β-Ga₂O₃ commercial substrates consisting of two sharp peaks at 689 nm and 697 nm superimposed on a broader peak centered at 710 nm originates from Cr impurities present at a concentration near 2 ppm. The red emission exhibiting a twofold symmetry, peaks in intensity for excitation near the absorption edge, seems to compete with the Ga₂O₃ emission at a higher excitation energy and appears to be intensified in the presence of Fe. Based on the polarized absorption, luminescence observations, and the Tanabe–Sugano diagram analysis, we propose a resonant energy transfer of photogenerated carriers in the $\beta$ -Ga₂O₃ matrix to octahedrally coordinated Cr³⁺ to give red luminescence, possibly also sensitized by Fe³⁺.