P A P E R    T I T L E
Gate Metallization Study for InGaP/InGaAs/GaAs pHEMTs

A U T H O R  /  C R E D I T S
P. Fay, K. Stevens * , J. Elliot * , and N. Pan *

Department of Electrical Engineering, University of Notre Dame, 275 Fitzpatrick Hall, Notre Dame, IN 46556
voice: (219) 631-5693, fax: (219) 631-4393 pfay@nd.edu
* Kopin Corporation, 695 Myles Standish Blvd., Taunton, MA 02780 (508) 824-6696

A B S T R A C T
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 ob-tained for Mo/Au, Ti/Au, and Pt/Au contacts, respectively. The electrical properties of 0.7µm 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.