| This study examines both the metallurgy and resistance analysis techniques for rapid thermal annealed Ohmic contacts to GaAs. First, the initial phases of contact formation are monitored through a kinetics analysis. Second, an in-depth look at the measurement of specific contact resistance is presented, based on data from extensive testing and rigorous theoretical considerations.;A new Rapid Thermal Annealing (RTA) technique has been developed which uses very small samples of low melting elements and eutectic alloys to standardize temperature measurements. Temperatures of thin films during anneal are shown to lie within ;Complex metallurgical reactions, similar to those characterized above, take place during time-temperature aging of the NiGeAu contact and limit its reliability. Therefore, we have examined alternate ohmic metallization systems which may have superior stability, including NiGeAs, PdGe, and PdInGe. Appropriated thin film metallurgy results are discussed. Both NiGeAu and PdInGe metallizations are implemented in a six mask MESFET process to produce ohmic contact test structures. Appropriate one dimensional analytic and two dimensional numerical analysis are performed based on data from the Transmission Line Model (TLM) and Cross-bridge Kelvin (CBK) resistor structures. A careful quantitative comparison, accounting for the presence of alignment tolerance induced parasitic resistances, shows that the one dimensional analysis drastically overestimates values for the specific contact resistance, thus contributing to the wide variation of such values often cited in current literature. We demonstrate that this effect is metallization independent, and must be accounted for in the design of future GaAs devices. |
