On the origin of red luminescence from iron-doped β-Ga_2O_3 bulk crystals

摘要

Currently, Fe doping in the ～10~(18) cm~(-3) range is the most widely available method for producing semi-insulating single crystalline β-Ga_2O_3 substrates. Red luminescence features have been reported from multiple types of Ga_2O_3 samples, including Fe-doped β-Ga_2O_3, and attributed to Fe or N_O. Herein, however, we demonstrate that the high-intensity red luminescence from Fe-doped β-Ga_2O_3 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 Ga_2O_3 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 photo-generated carriers in the β-Ga_2O_3 matrix to octahedrally coordinated Cr~(3+) to give red luminescence, possibly also sensitized by Fe~(3+).