Performance of Pd/Ge/Au/Pd/Au ohmic contacts and its application to GaAs metal-semiconductor field-effect transistors

Pd/Ge/Au/Pd/Au ohmic contacts have been studied for application to GaAs met al-semiconductor field-effect transistors (MESFETs). The interfacial reacti on of the Pd/Ge/Au/Pd/Au ohmic contact is investigated using X-ray diffract ion, Auger depth profile, and scanning electron microscopy. The good Pd/Ge/ Au/Pd/Au ohmic contact with the lowest contact resistivity of similar to 2 x 10(-6) Omega cm(2) is obtained after annealing at 400 degrees C. This is due to formation of AuGa compound through in-diffusion of Au toward the GaA s substrate. The AuGa compound enhances creation of more Ga vacancies, foll owed by incorporation of Ge into the Ga vacancies, and it allows the contac t to be formed directly on the GaAs layer. The contacts were also thermally stable after isothermal annealing at 400 degrees C for 3 h. The fabricated device has a pinch-off voltage of -0.62 V. The maximum drain current densi ty measured at V-gs = 10.4 V, was 41 mA mm(-1). The transconductance was 27 4 mS mm(-1) for the gate voltage of 0 V. This supports the fact that the Pd /Ge/Au/Pd/Au ohmic contact is suitable for application to GaAs MESFETs due to its law-resistance characteristics and good surface morphology. (C) 1999 Elsevier Science Ltd. All rights reserved.