Oxides and nitrides, such as sapphire (Al2O3) and gallium oxide (Ga2O3), are considered to be wide bandgap insulators. In these materials, the high energy electron beam of an electron microscope offers an ideal tool to study the electronic and optical properties without the need to resort to specialized deep ultraviolet lasers for photoluminescence. Cathodoluminescence (CL) is useful to determine the energy bandgap and to reveal the presence (and energy state) of electrically active defects. This makes it a preferred tool to study the basic optical properties of these materials as well as discriminate between different phases of compositionally and chemically identical materials, e.g., the anatase and rutile phases of TiO2.

Recently, β-Ga2O3 receives increased attention due to its intrinsic ultra-wide bandgap and optical transparency in visible light, implying a natural application to solar-blind ultraviolet (UV) photodetection. There are limited techniques to determine material quality and characterize the defects that may be present. CL is one such a technique—CL spectroscopy has been used to reveal oxygen vacancy-related and (two) gallium vacancy-related energy levels within the β-Ga2O3 bandgap, including spectral changes associated with removing or creating these defects through materials processing. These defect levels compete with the near band edge luminescence and the relative ration of the two luminescence types provides insight into material quality.