Assessment of bonding characteristic of -(Al_xGa_1-x)₂O₃ alloys from photoluminescence and x-ray absorption near edge spectroscopy

Bonding characteristics of the beta-(AlxGa1-x)(2)O-3 alloy have been assessed from red luminescence and x-ray absorption near edge spectroscopy (XANES). Red luminescence, known as R1 and R2 lines, originates from crystal field split d-levels of unintentionally present Cr3+ ions in the beta-(AlxGa1-x)(2)O-3 alloy, is found to blueshift with Al composition. This indicates that the nephelauxetic effect in beta-Ga2O3 materials decreases with Al substitution, which results to a decrease in the covalency of the beta-(AlxGa1-x)(2)O-3 alloy. The XANES experiments at the oxygen K-absorption edge provide clear evidence of the decrease in the covalency of the alloy, where an absorption peak representing the covalency in the beta-Ga2O3 material is found to decrease with an increase in the Al composition. Furthermore, the nature of the observed red luminescence for the beta-(AlxGa1-x)(2)O-3 alloy is determined to be excitonic recombination. Our results further confirm the fact that the red luminescence from Cr3+ ions is an excellent local probe to assess the bonding characteristic of the host material.