Persistent Room-Temperature Photodarkening in Cu-Doped β-Ga2O3

beta-Ga2O3 is an ultrawide band gap 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 beta-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 (H-i) 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.

Automated summary

This study finds that exposure of Cu-doped beta-Ga2O3 to UV light (>4 eV) causes large, persistent photo induced darkening at room temperature. Light exposure converts Cu2+ to Cu3+ and leads to the appearance of O-H vibrational modes. Cu acceptors can form favorable complexes with hydrogen donors, and when these complexes absorb light, hydrogen is released, resulting in the formation of Cu3+ species and O-H modes.