Backside secondary ion mass spectrometry investigation of ohmic and Schottky contacts on GaAs

A backside secondary ion mass spectrometry (SIMS) technique is employed to examine seven distinctive metallic contacts on GaAs at various stages of formation. The contacts are formed on multilayered GaAs/AlGaAs structures grown by molecular beam epitaxy (MBE), each containing an AlGaAs etch‐stop layer and AlGaAs marker layers for precise alignment of the SIMS depth profiles. After removal of the substrate, the contact structures are profiled from the backside to avoid depth resolution degradation, which results when sputtering through a nonuniform multilayered metallic contact. The seven contacts examined are TaSix, Au/Ge/Ni, Au/Ge/Pd, Ge/Pd, Si/Pd, In/Pd, and Si/Ni/Mg. The TaSix Schottky contact exhibits extensive interdiffusion. The Au/Ge/Ni contact reveals extensive GaAs consumption. Much less consumption occurs in the Au/Ge/Pd contact. The absence of Au in the Ge/Pd contact leads to an extremely abrupt contact interface, with the Ge concentration dropping by four orders of magnitude within ∼100 A of t...