Process Optimization for a Transimpedance Pre-Amplifier Using Self-Aligned GaAs MESFETs on Epitaxial Wafers

Fabrication of self-aligned n-channel GaAs MESFETs has been carried out for realization of a transimpedance amplifier. The critical process steps e.g. the gate recess etch and ohmic and Schottky contact metallizations have been optimized. The behaviour of ohmic and Schottky contacts with different annealing temperatures and times has been studied. Our experiments show that best characteristics for a MESFET can be obtained over a relatively narrow range of annealing temperatures and times than reported for both ohmic and Schottky contacts annealed together. The variation of etch rates for various window sizes used for gate recess etching of n-GaAs in wet chemical etchant is also studied. Complete fabrication process flow is optimized by studying these effects. A transimpedance preamplifier is fabricated based on the optimized process and characterized.