Gallium nitride (GaN) has been considered one of the most promising materials for the next-generation power and radio-frequency electronic devices, as they can operate at higher voltage, higher frequency, and higher temperature, compared with their silicon (Si) counterparts. However, the fresh GaN surface is susceptible to the natural oxidation composed of Ga2O3, Ga2O, and other intermediate oxidation states. Moreover, the oxidized GaN surface no longer features the distinct atomic step-terrace morphology, resulting in a degraded interface when gate or passivation dielectrics are deposited without appropriate pretreatment. It is responsible for the degraded performance of GaN-based devices such as current collapse and threshold voltage instability. In this study, the proposed high-temperature (500 °C) remote plasma pretreatments (RPPs) can play a significant role in addressing the issue of the deteriorated GaN surface exposed to air. Atomic step-terrace morphology was recovered after 500 °C-RPP due to the removal of oxides and suboxides. First-principles calculations verified that Ga2O at the GaN surface leads to interface states at ∼2.9 eV (EC-E ∼ 0.4 eV) in the bandgap, which is consistent with the increase of interface states at the EC-E range of 0.4-0.9 eV measured through constant-capacitance deep-level transient spectroscopy. Meanwhile, deep interface states and surface-related current collapse are well suppressed in GaN metal-insulator-semiconductor devices. These improved properties by 500 °C-RPP are generalizable to a broader range, including pre-gate and pre-passivation treatment, of which a decent surface/interface is desirable for high-performance GaN-based devices.
Keywords: Ga2O removal; atomic step; current collapse; interface states; remote plasma pretreatment.