Controllable Thin-Film Approaches for Doping and Alloying Transition Metal Dichalcogenides Monolayers

Abstract

Two-dimensional (2D) transition metal dichalcogenide (TMD) monolayers exhibit exciting properties and versatile material chemistry promising for device miniaturization, energy, quantum information science, and flexible optoelectronics. Their outstanding structural stability permits a variety of foreign dopants that can modulate their optical and electronic properties and induce phase transition, thereby adding new functionalities such as magnetism, ferroelectricity, quantum states. To accelerate their technological readiness, it is essential to develop controllable synthesis and processing techniques to precisely engineer the compositions and phases of 2D TMDs. While most reviews emphasize properties and applications of doped TMDs, here, we report recent progress on thin-film techniques that show excellent controllability for substitutional doping of 2D TMDs. These techniques are categorized into bottom-up methods that grow doped samples on substrates directly and top-down methods that use an energetic source to implant dopants into existing 2D crystals. The doped and alloyed variants from the group-VI semiconducting TMDs will be at the center of technical discussions, as they are expected to play essential roles in next-generation optoelectronic applications. A theoretical background based on first principles calculations will precede the technical discussions to help the reader understand each element’s likelihood of substitutional doping and their impact on the electronic properties.