Surface Ga-boosted Boron-doped $\mathrm{Si}_{0.5}\mathrm{Geo}_{0.5}$ using In-situ CVD Epitaxy: Achieving $1.1 \times 10^{21}\mathrm{cm}^{-3}$ Active Doping Concentration and $5.7\times 10^{-10}\Omega-\mathrm{cm}^{2}$ Contact Resistivity

For the first time, we have achieved contact resistivity $(p_{c}$ ) less than 10 −9 Ω-cm 2 for p-type metal/Si 1-x Ge x contacts with in-situ doping-only technique. This is enabled by an optimized surface Gallium (Ga)-boosted Boron (B)-doped $\mathrm{Si}_{0.5}\mathrm{Ge}_{0.5}$ having active doping concentration $(N_{a})$ of $1.1 \times 10^{21}$ cm −3 grown using reduced pressure chemical vapour deposition (RPCVD). Compared with B-only doped sample with $N_{a}$ of $9\times 10^{20}\mathrm{cm}^{-3}$ B and Ga codoping enhances $N_{a}$ by $2\times 10^{20} \mathrm{cm}^{-3}$ reducing $\rho_{c}$ from $1.5\times 10^{-9}\Omega-\mathrm{cm}^{2}$ to 5.7 $\times 10^{10}\Omega-\mathrm{cm}^{2}.\ \rho c$ was extracted using advanced ladder transmission line model (LTLM) structures. It was also found that sub- $10^{9}\Omega-\mathrm{cm}^{2}\rho_{c}$ of our $\mathrm{Ti}/\mathrm{Si}_{0.5}\mathrm{Ge}_{0.5}$ contact can be maintained with thermal budget up to 450°C.