CHEMICAL-REACTIONS AT METAL COMPOUND SEMICONDUCTOR INTERFACES - AU AND GAAS

The reaction between Au thin films and GaAs substrates is discussed. The reaction proceeds by dissolution of the GaAs to form a Au-Ga solid solution, but regrowth of GaAs at the Au/GaAs interface is occurring simultaneous with dissolution. The rate of this reaction depends upon the condition of the GaAs surface at the interface. Contrary to most systems, thin native oxides increase the rate of the reaction while oxide-free interfaces react more slowly. Sputter damaged, oxide-free interfaces react at an intermediate rate. Dopant from the substrate may segregate to the decomposed GaAs areas leading to the formation of an ohmic contact after reaction. Finally, heating sandwich structures of Au-Ge, As and Ga on GaAs to approximately 400-degrees-C results in isothermal regrowth of doped, smooth, planar ohmic contacts with low specific contact resistance. This procedure should be suitable for forming ohmic contacts on shallow junction devices.