Assessment of bonding characteristic of β-(AlxGa1−x)2O3 alloys from photoluminescence and x-ray absorption near edge spectroscopy

Abstract

Bonding characteristics of the β-(AlxGa1−x)2O3 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 β-(AlxGa1−x)2O3 alloy, is found to blueshift with Al composition. This indicates that the nephelauxetic effect in β-Ga2O3 materials decreases with Al substitution, which results to a decrease in the covalency of the β-(AlxGa1−x)2O3 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 β-Ga2O3 material is found to decrease with an increase in the Al composition. Furthermore, the nature of the observed red luminescence for the β-(AlxGa1−x)2O3 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.

Effect of Al substitution on the electron-phonon interaction for β-Ga2O3

“…It has been reported that the ionicity (bond length) of the β-(Al x Ga 1-x ) 2 O 3 alloy increases (decreases) [43] with the Al composition. Hence, one may expect that the e-ph interaction strength and the mean phonon temperature should increase with the Al composition.…”