Annealing behaviour of Au/LaB6/Au/Ni/Ge systems on n-GaAs studied by the SNMS technique

Interdiffusion and microstructural properties of sophisticated ohmic contacts on n-GaAs containing diffusion barriers are studied by SNMS. In detail the metallization systems Au/LaB6/Au/Ni/Ge and Au/LaB6/Ni/Ge are investigated. It is found that the blocking behaviour of the LaB6 barrier depends on the amount of oxygen that has been introduced into the barrier during deposition. In a non-optimized barrier, grain boundary diffusion from the gold top layer through the LaB6 barrier to the internal Au/Ni/Ge metallization system takes place. This significantly changes the chemical composition and thus the electrical behaviour of the contact. Grain boundary diffusion is inhibited by incorporating oxygen into the LaB6 diffusion barrier. This results in contact systems that are stable against diffusion from the gold top layer.