Origin of interfacial charges of Al₂O₃/Si and Al₂O₃/GaN heterogeneous heterostructures

Al₂O₃ is a broadly employed dielectric and significant interfacial charges occur at Al₂O₃/semiconductor interfaces. However, the charge origin is often unclear that severely impacts device engineering and design. Al₂O₃/Si and Al₂O₃/GaN are two of the most common heterogeneous heterostructures (H2s) for many crucial devices including GaN transistors and Si solar cells. While negative charges are extensively observed in Al₂O₃/Si, positive charges exist in Al₂O₃/GaN, both of which are not well understood. In this study, we performed in-depth interfacial studies of the Al₂O₃/Si and Al₂O₃/GaN H2s to clarify the origin of the interfacial charges. Stoichiometry deviations were found at the interfaces of the two H2s where Al surpasses O for Al₂O₃/GaN, whereas O dominates at the Al₂O₃/Si interface. Therefore, we propose that the different interfacial charges are caused by nonstoichiometry atomic ratios of Al₂O₃ at the interface. The study indicates the important role of the semiconductor surface on the device performance, provide a deep understanding on the origin of interfacial charges at the insulator-semiconductor interfaces.