Defects in – and on – Gallium Oxide

Monoclinic gallium oxide (β-Ga₂O₃) is an ultra-wide bandgap semiconductor with potential applications in power electronics. Semi-insulating substrates are required for most practical devices such as metal-oxide-semiconductor field effect transistors. Defects in and on these substrates will affect the performance of device structures grown on them. This presentation will discuss recent experimental studies on Czochralski-grown β-Ga₂O₃ single crystals doped with Mg, Zn, and Cu acceptors. While Mg and Zn result in semi-insulating material, Cu exhibits the unexpected property of persistent photodarkening. In addition to defects in the bulk, spectral microscopy has revealed several specific defects on the surface. Some of these localized centers are very bright UV emitters. By combining photoluminescence and Raman spectroscopy, intriguing clues are being found about the identity of these mysterious surface defects.