Persistent room temperature photodarkening in Cu-doped \b{eta}-Ga2O3

TL;DR

This study demonstrates that UV light exposure causes persistent room temperature photodarkening in Cu-doped beta-Ga2O3, linked to Cu oxidation state changes and hydrogen interactions, impacting its optoelectronic properties.

Contribution

It reveals the mechanism of photodarkening in Cu-doped beta-Ga2O3 involving Cu oxidation and hydrogen complexation, a novel insight into defect-related optical behavior.

Findings

UV light induces persistent darkening at room temperature.

Cu2+ converts to Cu3+ upon light exposure, causing optical absorption.

Hydrogen release from Cu-H complexes contributes to the darkening.

Abstract

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.