Tungsten silicide Schottky contacts on GaAs

Two types of I–V characteristics for W–Si/GaAs Schottky contacts have been observed. With sputtering deposition from a W–Si composite target (type A), The Schottky contacts have a Schottky barrier height ΦB of 0.64 V and an ideality factor, n of 1.05. The I–V behavior is independent of the WSix composition for x=0.42–2.3. With cosputtering from W and Si targets (type B), an excellent WSi0.6/GaAs Schottky contact is obtained with ΦB equal to 0.8 V and an ideality factor equal to unity. The I–V characteristics of both types of diodes agree with the theoretical thermionic-emission model for both forward and reverse bias. For type B diodes, high-temperature stability has been demonstrated with furnace annealing up to 750 °C. In previous studies, composition of the W–Si film has been emphasized as the single most important factor for GaAs Schottky gates. Our work has shown, besides silicide composition, surface cleaning procedures and silicide deposition techniques will have a greater effect on the diode I–V characteristics, the thermal stability of the Schottky contact, and the silicide adhesion on GaAs substrate. Sputter etching of the GaAs substrate prior to silicide deposition can improve the silicide adhesion up to a heat treatment of 1000 °C but with a degradation of diode performance. A negative substrate bias during deposition was shown to be a better compromise for both adhesion and electrical considerations.