Degradation Mechanism of Ge N⁺-P Shallow Junction with Thin GeSn Surface Layer

In this article, the degradation mechanism of the Ge N⁺-P junctions with a thin GeSn surface layer is investigated, aiming for source/drain (S/D) application in emerging field-effect transistors. GeSn is a promising channel material with high carrier mobility, which can offer a better performance of the field-effect transistors. By performing thermal annealing at different temperatures, the reverse-biased leakage current increases apparently when annealing temperature exceeds 550 °C. X-ray diffraction (XRD) analysis indicates most Sn atoms escape from lattice sites while secondary-ion mass spectroscopy (SIMS) analysis indicates enhanced Sn diffusion in Ge bulk after ion implantation. Therefore, a degradation model considering Sn-defects interaction is proposed to explain the degradation of junction leakage current and possible solution is proposed.