Low-Resistance and Thermally Stable Ohmic Contacts on n-GeSn Using Ni and Ti Metallization

The development of suitable contacts for n-doped GeSn is a critical challenge to fully realize the potential of GeSn-based devices. Here, we have used transfer length method (TLM) measurements to investigate the contact properties of n-doped GeSn films with 6% of Sn after different types of metallization (with Ni, Ni0.9Pt0.1, and Ti). We also quantified the impact of different surface precleaning methods on contact formation. We successfully achieved ohmic contacts for all metallizations and measured contact resistivities as low as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-{5}}~\Omega \cdot $ </tex-math></inline-formula>cm2. Ni-based contacts showed stability up to <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, while Ti-based contacts exhibited superior thermal stability (at least on the time scale of contact formation annealing), maintaining performance up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400~^{\circ }$ </tex-math></inline-formula>C. While Ti has been used to contact p-doped GeSn films, this work represents the first exploration of its applicability to n-doped films.