NIGE-BASED OHMIC CONTACTS TO N-TYPE GAAS .1. EFFECTS OF IN ADDITION

Contact resistances of NiGe ohmic contacts, which had been previously developed in our laboratory, were reduced significantly by adding a sm all amount of In to the NiGe contacts without deteriorating the therma l stability, the surface smoothness, and the shallow diffusion depth. The optimum layer thicknesses to prepare the low resistance ohmic cont acts were determined to be 60 nm for Ni, 100 nm for Ge, and 3 nm for I n, and the contact resistances (R(c)) less than 0.3 fl mm were obtaine d after annealing at temperatures in the range between 600 and 700-deg rees-C. Microstructural analysis at the GaAs/metal interface of the co ntact with low R(c) showed formation of ''regrown'' GaAs and InxGa1-xA s layers between the GaAs substrate and high melting point NiGe compou nds. Based on the present electrical measurements and microstructural analysis, a model for the current transport of the NiGe-based ohmic co ntacts was proposed, which explained well the dependencies of the cont act resistances on the microstructure at the GaAs/metal interface.