ABSTRACT: 2D semiconductors are one of the most promising materials to overcome Moore's law limitations for next generation electronics. High-quality wafer-scale 2D semiconductors is the precondition to realize the scalable application in the high-end integrated circuits (IC) field. However, it is still a great challenge in the growth of continuous 2D monolayer semiconductor with single crystalline structure at wafer scale. We developed an epitaxial phase conversion (EPC) process to meet this requirements.
The EPC process is a kind of two-step process, where sulfurization process was carried out on pre-deposited Mo-containing films. Traditionally, two-step processes for 2D MoS2 and other chalcogenides have suffered poor quality film and non-discontinuity at monolayer thickness. The reason was regarded as the poor lattice quality of precursor film. The EPC process solves these problems by carefully preparing precursor film and carefully controlling sulfurization process. The precursor film we selected is high-quality epitaxial MoO2 grown on 2" diameter sapphire substrate by pulsed laser deposition. This epitaxial precursor contains significantly fewer defects compared to amorphous precursor films, thus fewer defects are inherited by the EPC MoS2 film. Thus, the EPC MoS2 film quality is much better. The EPC prepared monolayer MoS2 devices show field effect mobility between 10 ~ 30 cm2·V-1s-1, which is the best among two-step process. We also developed a capping layer annealing process (CLAP) method to further reduce the defects in the precursor oxide film, thus in-plane texture in the thicker MoS2 film was eliminated and single-crystalline structure was obtained. The potential feasible technique to further improve the 2D film quality is pointed out for our next research plan. In the meanwhile, the EPC process we developed is proposed to be a universal growth method. Last but not least, we also proposed several potential applications of the wafer-scale single-crystalline MoS2 film we developed, such as logic circuits, flexible electronics and seeding layer of van der Waal or remote epitaxial growth.