Effect of Gate Sinking on the Device Performance of the InGaP/AlGaAs/InGaAs Enhancement-Mode PHEMT

An enhancement-mode InGaP/AlGaAs/InGaAs pseudomorphic high-electron mobility transistor using platinum (Pt) as the Schottky contact metal was investigated for the first time. Following the Pt/Ti/Pt/Au gate metal deposition, the devices were thermally annealed at 325 degC for gate sinking. After the annealing, the device showed a positive threshold voltage (V_th) shift from 0.17 to 0.41 V and a very low drain leakage current from 1.56 to 0.16 muA/mm. These improvements are attributed to the Schottky barrier height increase and the decrease of the gate-to-channel distance as Pt sinks into the InGaP Schottky layer during gate-sinking process. The shift in the V_th was very uniform across a 4-in wafer and was reproducible from wafer to wafer. The device also showed excellent RF power performance after the gate-sinking process