Zhihua Dong

We performed dry oxidation on n-type silicon carbide (SiC), followed by annealing in diluted N₂O, and subsequently fabricated n-type MOS structures. The study aimed to investigate the impact of different annealing times on the trap charges near the SiC/SiO₂ interface and the reliability of the gate dielectric. Capacitance-voltage (C-V) and current-voltage (I-V) measurements of the n-type MOS revealed that increasing the annealing time with N₂O effectively reduces the density of electron traps near the SiC/SiO₂ interface, mitigates the drift in flat-band voltage and enhances the oxide breakdown field strength. However, excessive annealing time leads to an increase in the flat-band voltage drift of the MOS, resulting in premature oxide breakdown. Using the optimized annealing conditions, we fabricated n-type LDMOSFETs and obtained the threshold voltage (Vth), field-effect mobility (μ_FE) and specific on-resistance (Ron-sp) from the transfer curve (Id-Vg) and output curve (Id-Vd) measurements. The research findings provide valuable insights for the gate oxidation process of SiC.

This letter reports the phenomenon of current drops in an AlGaN/GaN heterojunction with CF₄ plasma treated in a polar gas ambient. Ungated AlGaN/GaN HEMT with CF₄ plasma treatment was tested in ethanol, acetonitrile, and an acetic acid gas ambient, and the current dropped by 52%, 51% and 61%, respectively, which are much higher than the drops (6%, 7%, and 8%) in normal ungated HEMT. On the one hand, based on “ambient doping”, a possible model was proposed to explain this phenomenon. On the other hand, the lower initial current was very important to increase the sensitivity. This means that the initial current should be elaborately designed to achieve maximum sensitivity.

This study has demonstrated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) on Si substrates with a SiN_x/SiON composite gate dielectric. The threshold voltage shift in the devices was investigated. The MIS-HEMTs with the SiN_x/SiON composite gate dielectric exhibited superior threshold voltage uniformity and small threshold voltage hysteresis than the reference device with SiN_x only gate dielectric. The variation of the device threshold voltage was mainly related to trapping process by the interface states, as confirmed by band diagrams of MIS-HEMTs at different gate biases. Based on frequency-dependent capacitance measurements, interface state densities of the devices with the composite and single gate dielectrics were extracted, where the former showed much smaller interface state density. These results indicate that the SiN_x/SiON composite gate dielectric can effectively improve the device performance of GaN-based MIS-HEMTs and contribute to the development of high-performance GaN electronic devices.