Ultralow-Thermal-Budget Processing for Electronic-Grade Metal Chalcogenides and Elemental Chalcogen Films

van der Waals coupled chalcogenides show a wealth of exotic physical phenomena when confined into the 2D lattice, and the relevant electronic devices thus far have defined themselves as a promising building block of nanoelectronics owing to the near-atom thickness, superior electrostatic control, and adaptable device architecture. This talk will highlight how such emerging materials can further benefit from ultralow-thermal-budget processing and new device configurations. I will mainly introduce vapor-phase synthetic strategy for wafer-scale, thickness-controlled, and low-temperature deposition techniques to bring such new electronic functionalities into device-level applications. To be specific, we demonstrate the wafer-scale growth of mono-elemental 2D tellurium (Te) thin films using an annealing-free, low-temperature ALD process. As-deposited Te films exhibit exceptional homogeneity, precise layer controllability, and 100 % step coverage in high aspect ratio nanostructures. As a 2D building block with intrinsic p-type transport characteristics, ALD-grown Te films are employed for fabricating 2D/2D and mixed-dimensional 2D/3D vertical p-n heterojunction diodes exhibiting well-defined current rectification. Additionally, we showcase an ALD-Te-based selector device with fast switching time, selectivity and low V_th. As a second example, we also developed phase-tailored synthetic strategies where we achieve wafer-scale production of tin selenides (SnSe and SnSe₂) in the 2D limit by utilizing a low-temperature MOCVD process. Directly grown 2D SnSe₂ exhibits outstanding crystallinity and tunable thickness of nm-precision, and SnSe, which has intrinsic limitations for 2D film growth, can be prepared via a thermally driven phase transition, thereby retaining all of the advantages in the MOCVD-grown product. With those developed low-temperature processing, I will share more recent progress toward BEOL-compatible low-power steep-slope switch and cryogenic nonvolatile memory devices, all based on synthetic chalcogenide thin films.