Beta-Ga2O3 is an ultra-wide bandgap semiconductor with emerging applications in power electronics. The introduction of acceptor dopants yields semi-insulating substrates necessary for thin-film devices. In the present work, exposure of Cu-doped Ga2O3 to UV light > 4 eV is shown to cause large, persistent photo-induced darkening at room temperature. Electron paramagnetic resonance spectroscopy indicates that light exposure converts Cu2+ to Cu3+, a rare oxidation state that is responsible for the optical absorption. The photodarkening is accompanied by the appearance of O-H vibrational modes in the infrared spectrum. Hybrid function calculations show that Cu acceptors can favorably complex with hydrogen donors incorporated as interstitial (Hi) or substitutional (H_O) defects. When Cu_Ga-H_O complexes absorb light, hydrogen is released, contributing to the observed Cu3+ species and O-H modes.
@article{arxiv.2201.01861,
title = {Persistent room temperature photodarkening in Cu-doped \b{eta}-Ga2O3},
author = {J. Jesenovec and C. Pansegrau and M. D. McCluskey and J. S. McCloy and T. D. Gustafson and L. E. Halliburton and J. B. Varley},
journal= {arXiv preprint arXiv:2201.01861},
year = {2022}
}