Record Low Contact Resistivity (4.4×10−10 Ω-cm2) to Ge Using In-situ B and Sn Incorporation by CVD With Low Thermal Budget (≤400°C) and Without Ga

The record low contact resistivity $(\rho_{\text{c}})$ of $4.4\text{x}10^{-10}\Omega-\text{cm}^{2}$ is achieved in Ti metal contact to in-situ B-doped $\text{GeSn}$ using B $(> 1\text{x}10^{21}\text{cm}^{-3})$ and Sn $(> 12\%)$ segregations at the Ti/GeSn:B interface. Sn incorporation into Ge lowers the Schottky barrier height of holes. Increasing B doping at the $\text{Ti}/\text{GeSn}:\text{B}$ interface reduces the hole tunneling distance. Thanks to the low growth temperature (305°C) of the chemical vapor deposition using Ge2H6, the GeSn:B with the bulk active [B] of $2.1\text{x}10^{20}\text{cm}^{-3} (>> > \text{the}$ solid solubility of B in $\text{Ge}=5.5\text{x}10^{18}\text{cm}^{-3}$) and the bulk [Sn] of 4.9% is successfully grown. Without the needs of the previously reported Ga dopants and the high temperature annealing for dopant activation, the record low $\rho_{\text{c}}$ is achieved with all the process temperatures $\leq 400^{\text{o}}\text{C}$.