Ultra-low Specific Contact Resistivity (3.2×10 -10 Ω-cm 2 ) of Ti/Si 0.5 Ge 0.5 Contact: Deep Insights into the Role of Interface Reaction and Ga Co-doping

We report an ultra-low specific contact resistivity (ρ c ) down to 3.2×10-10 Ω-cm2 on in-situ grown boron (B) and surface segregated gallium (Ga) co-doped p+-Si 0.5 Ge 0.5 with a high average active doping concentration (N A ) of 1.2×1021 cm-3. Two batches of devices with 8 sets of data using ladder transmission line model (LTLM) were fabricated to confirm the accuracy. We also found, for the first time, that the co-doped Ga not only enhances N A but also plays a vital role in achieving thermally stable Ti/p+-Si 0.5 Ge 0.5 contacts with the thermal budget of up to 450 °C. A mechanism for the deep understanding of such phenomenon was proposed and experimentally verified.