Fixed charge and trap states of in situ Al₂O₃ on Ga-face GaN metal-oxide-semiconductor capacitors grown by metalorganic chemical vapor deposition

In situ Al₂O₃ on Ga-face GaN metal-oxide- semiconductor capacitors (MOSCAPs) were grown by metalorganic chemical vapor deposition and measured using capacitance-voltage techniques. The flat band voltage and hysteresis had a linear relationship with Al₂O ₃ thickness, which indicates the presence of fixed charge and trap states that are located at or near the Al₂O₃/GaN interface. In addition, slow and fast near-interface states are distinguished according to their different electron emission characteristics. Atom probe tomography was used to characterize the in situ MOSCAPs to provide information on the Al/O stoichiometric ratios, Al₂O₃/GaN interface abruptnesses, and C concentrations. The in situ MOSCAPs with Al ₂O₃ deposited at 700 °C exhibited an order of magnitude higher fast near-interface states density but a lower slow near-interface states density compared with those with Al₂O ₃ deposited at 900 and 1000 °C. Furthermore, the 700 °C MOSCAPs exhibited a net negative fixed near-interface charge, whereas the 900 and 1000 °C MOSCAPs exhibited net positive fixed near-interface charges. The possible origins of various fixed charge and trap states are discussed in accordance with the experimental data and recently reported first-principals calculations.