Defect-Mediated Phase Transformation in Anisotropic Two-Dimensional PdSe 2 Crystals for Seamless Electrical Contacts.

The failure to achieve stable Ohmic contacts in two-dimensional material devices currently limits their promised performance and integration. Here we demonstrate that a phase transformation in a region of a layered semiconductor, PdSe ₂ , can form a contiguous metallic Pd ₁₇ Se ₁₅ phase, leading to the formation of seamless Ohmic contacts for field-effect transistors. This phase transition is driven by defects created by exposure to an argon plasma. Cross-sectional scanning transmission electron microscopy is combined with theoretical calculations to elucidate how plasma-induced Se vacancies mediate the phase transformation. The resulting Pd ₁₇ Se ₁₅ phase is stable and shares the same native chemical bonds with the original PdSe ₂ phase, thereby forming an atomically sharp Pd ₁₇ Se ₁₅ /PdSe ₂ interface. These Pd ₁₇ Se ₁₅ contacts exhibit a low contact resistance of ∼0.75 kΩ μm and Schottky barrier height of ∼3.3 meV, enabling nearly a 20-fold increase of carrier mobility in PdSe ₂ transistors compared to that of traditional Ti/Au contacts. This finding opens new possibilities in the development of better electrical contacts for practical applications of 2D materials.