Advanced defect spectroscopy in wide-bandgap semiconductors: review and recent results

The study of deep-level defects in semiconductors has always played a strategic role in the development of electronic and optoelectronic devices. Deep levels have a strong impact on many of the device properties, including efficiency, stability, and reliability, because they can drive several physical processes. Despite the advancements in crystal growth, wide- and ultrawide-bandgap semiconductors (such as gallium nitride and gallium oxide) are still strongly affected by the formation of defects that, in general, can act as carrier traps or generation-recombination centers (G-R). Conventional techniques used for deep-level analysis in silicon need to be adapted for identifying and characterizing defects in wide-bandgap materials. This topical review paper presents an overview of reviews of the theory of deep levels in semiconductors; in addition, we present a review and original results on the application, limits, and perspectives of two widely adopted common deep-level detection techniques, namely capacitance deep-level transient spectroscopy and deep-level optical spectroscopy, with specific focus on wide-bandgap semiconductors. Finally, the most common traps of GaN and beta-Ga2O3 are reviewed.