Low-Temperature Processed Ni/GeSn Optimal Contacts for Junctionless GeSn_-on-Si FinFETs

For junctionless FETs (JLFETs), an optimal ohmic contact is needed to achieve maximum drive current. The scaling of the source/drain (S/D) contact area impacts the contact resistivity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho _{c}$ </tex-math></inline-formula>) of FETs, which limits their<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> current and switching speed. Minimizing the S/D series resistance along with ohmic contacts is the critical factor in JLFET design due to moderate doping levels at S/D. The Ni and Ge contacts optimized at a low temperature of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$350~^{\circ }$ </tex-math></inline-formula>C by forming gas annealing (FGA) process and the computed contact resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{c}$ </tex-math></inline-formula>), sheet resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {sh}}$ </tex-math></inline-formula>), and contact resistivity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho _{c}$ </tex-math></inline-formula>) for Ni/p-GeSn contacts are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.04\times 10^{-{3}}~\Omega \cdot \text {cm}$ </tex-math></inline-formula>, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$63.96~\Omega $ </tex-math></inline-formula>/□, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.18\times 10^{-{8}}~\Omega \cdot \text {cm}^{{2}}$ </tex-math></inline-formula>, respectively. The impact of capping metal resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{m}$ </tex-math></inline-formula>) is analytically examined for Ni/p-GeSn contacts using the modified circular transmission line model (cTLM). Furthermore, to study the metal cap resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{m}$ </tex-math></inline-formula>) effect pragmatically, the optimized GeSn channel FinFET with width/length (W/L) 20/90 nm is analyzed by incorporating an extra metal cap at contacts and its electrical characteristics were compared with the control sample. The result demonstrate that the effect of metal resistance is very significant in low sheet resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {sh}}$ </tex-math></inline-formula>) materials, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {sh}}$ </tex-math></inline-formula> is close to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{m}$ </tex-math></inline-formula>.