Contact resistances of NiGe ohmic contacts, which had been previously developed in our laboratory, were reduced significantly by adding a small amount of In to the NiGe contacts without deteriorating the thermal stability, the surface smoothness, and the shallow diffusion depth. The optimum layer thicknesses to prepare the low resistance ohmic contacts were determined to be 60 nm for Ni, 100 nm for Ge, and 3 nm for In, and the contact resistances (Rc) less than 0.3 OHgr; mm were obtained after annealing at temperatures in the range between 600 and 700 °C. Microstructural analysis at the GaAs/metal interface of the contact with lowRcshowed formation of ‘‘regrown’’ GaAs and InxGa1−xAs layers between the GaAs substrate and high melting point NiGe compounds. Based on the present electrical measurements and microstructural analysis, a model for the current transport of the NiGe‐based ohmic contacts was proposed, which explained well the dependencies of the contact resistances on the microstructure at the GaAs/metal interface.
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