Gate Metallization Study for InGaP/InGaAs/GaAs pHEMTs

The results of a gate metallization study for InGaP/InGaAs/GaAs pHEMTs are reported. Schottky contacts with Mo/Au, Ti/Au, and Pt/Au metallizations on InGaP lattice matched to GaAs are fabricated and barrier heights of 0.603, 0.621, and 0.738 eV are obtained for Mo/Au, Ti/Au, and Pt/Au contacts, respectively. The electrical properties of 0.7 μm gate length pHEMTs fabricated with each of these metallizations as the gate contact is also reported. Threshold voltage, transconductance, ft, and fmax are all found be influenced more strongly by the choice of gate metallization than can be explained by the difference in Schottky barrier height alone. A simple model that accurately accounts for the performance differences between the fabricated pHEMTs based on reduced effective gate-to-channel spacing is presented. Devices with Ti/Au gates exhibited an effective gate-to-channel spacing that was 17.5 Å smaller than identically-processed Mo/Au gate devices, while Pt/ Au gate devices exhibited effective gate-to-channel spacings 47.8 Å smaller than those of Mo/Au devices.