High-performance AlGaAs/GaAs MODFET'S with improved ohmic contacts

Alloyed ohmic contacts based on AuGeNiAg metallization with transfer resistance from ohmic metal to the 2DEG channel of less than 0.1 Ω mm have been fabricated on AlGaAs/GaAs MODFET layer structures. A sequential alloy technique was used to determine an optimum thermal alloy cycle for use on high-speed logic MODFET device layers. The resulting smooth surface morphology and extremely straight edges facilitate easy realignment for an all direct-write electron-beam lithographic process. Using saturated resistor loads, 5- and 11-stage ring oscillators were designed, fabricated, and tested. A minimum propagation delay as small as 22.2 ps/stage with a power dissipation of 1.22 mW/stage at a supply bias voltage of 1.35 V was achieved using this process.