From our study, we performed an oxygen-plasma pre-gate treatment on AlGaN/GaN HEMT deivce and found that Schottky height lowering after oxygen treatment was ascribed to surface states in AlGaN barrier layer near gate region that might cause output impedance variation, output power degradation and reliability issue. The surface defect traps with a shallow trapping level near gate region are responsible for triggering the behavior of parasitic resistance change. Also, these shallow traps easily generate electron emission current via a trap-assisted process, which can contribute an additional gate leakage current. Thus, such process-induced defect issue may play an important role to affect transistor output characteristics, especially for RF characteristics such as cut-off frequency and RF power gain.
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