Formation of WSi-based ohmic contacts to n-type GaAs

An outcome of the indirect doping concept conceived recently in NiGe-based Ohmic contacts has led to the development of annealed WSi-based Ohmic contacts to n-type GaAs for the first time. It was concluded that simultaneous addition of a “direct doping element” of Si in WSi_2.7 and an “indirect doping element (M)” such as Au, Pd, Cu, or Ag, was essential. The M(5 nm)/WSi_2.7(20nm)/W(50 nm) contacts showed Ohmic behavior after annealing with the lowest contact resistances of 0.4 Ω mm (6×10⁻⁶ cm²). In addition, the WSi-based contacts with a small amount of Au showed good thermal stability at 400 °C after contact formation. Microstructural analysis of the WSi contacts with Au showed formation of β-AuGa and WSi₂ compounds, which indicates that the Ohmic behavior would be due to heavy doping of Si at the GaAs surface induced by Ga out-diffusion. The mechanism of Ohmic contact formation of the present contacts agreed very well with that of the NiGe-based Ohmic contacts.