Novel Cu/Cr/Ge/Pd Ohmic Contacts on Highly Doped n-GaAs

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°C, the specific contact resistance of the copper-based ohmic contact Cu/Cr/Ge/Pd was measured to be (5.1 ± 0.6) × 10 −7 Ω 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°C annealing. However, after 400°C annealing, the reaction of copper with the underlying layers started to occur and formed Cu 3 Ga, Cu 3 As, Cu 9 Ga 4 , and Ge 3 Cu phases due to interfacial instability and copper diffusion.