Ultra-low Specific Contact Resistivity (3.2×10-10 Ω-cm2) of Ti/Si0.5Ge0.5 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-cm
²
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 1.2×10
²¹
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.