Oxides, nitrides, and other ceramics are typically wide bandgap materials regarded to as insulators. These materials, like sapphire (Al2O3) and gallium oxide (Ga2O3) contain various point and structural defects, as well as impurities. These defects and impurities provide a mechanism for the production of cathodoluminescence as free carriers generated by the electron beam recombine via the energy states inserted into the crystal's forbidden bandgap. By characterizing the radiative recombination of electron beam excited electron-hole pairs, cathodoluminescence can reveal the presence and type of defects or impurities present, as well as the material phase.

Spectroscopic analysis of ultra-wide bandgap semiconductors