Novel Cu/Cr/Ge/Pd ohmic contacts on highly doped n-GaAs

Abstract

The thermal stability of the Cu/Cr/Ge/Pd/n(+)-GaAs contact structure was evaluated. In this structure, a thin 40 nm layer of chromium was deposited as a diffusion barrier to block copper diffusion into GaAs. After thermal annealing at 350 degrees C, the specific contact resistance of the copper-based ohmic contact Cu/Cr/Ge/Pd was measured to be (5.1 +/- 0.6) x 10(-7) Omega cm(2). Diffusion behaviors of these films at different annealing temperatures were characterized by metal sheet resistance, X-ray diffraction data, Auger electron spectroscopy, and transmission electron microscopy. The Cu/Cr/Ge/Pd contact structure was very stable after 350 degrees C annealing. However, after 400 degrees C annealing, the reaction of copper with the underlying layers started to occur and formed Cu3Ga, Cu3As, Cu9Ga4, and Ge3Cu phases due to interfacial instability and copper diffusion.