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 metal-semiconductor field-effect transistors (MESFETs). The interfacial reaction of the Pd/Ge/Au/Pd/Au ohmic contact is investigated using X-ray diffraction, 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 GaAs substrate. The AuGa compound enhances creation of more Ga vacancies, followed by incorporation of Ge into the Ga vacancies, and it allows the contact 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 density measured at V-gs = 10.4 V, was 41 mA mm(-1). The transconductance was 274 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.