Abstract

Recently, atomically thin two-dimensional (2D) semiconductors have garnered substantial interest due to their unique optical and electrical properties. These exceptional attributes, including high electron mobility and superior optical absorption, making them as promising candidates for next-generation optoelectronic devices, logic circuits, and integrated circuits. Currently, chemical vapor deposition (CVD) is regarded as the most prevalent technique for synthesizing large-area and uniform 2D materials. However, the mobility of the 2D materials prepared from CVD methods still remains relatively low, which hinders their practical applications. Therefore, it is significant to grow 2D materials with high-mobility which are crucial for 2D electronics from lab to fab.

In this thesis, we devoted to growing high-mobility 2D materials by CVD for high-performance optoelectronics. We first synthesized the 2D air stable Bi₂O₂Te nanosheets using the low-pressure CVD method. The as-prepared Bi₂O₂Te single crystal device exhibited a Hall mobility of 496 cm²V^–1s^–1at 300 K, which reached 5000 cm²V^–1s^–1 at 2K. We then demonstrated a CVD method for synthesizing 2D Bi_xO_ySe_z materials at the wafer-scale. Wafer-scale 2D Bi₂O₂Se and Bi₃O_2.5Se₂ film can be achieved by adjusting the growth temperature, respectively. The Bi₂O₂Se₂ and Bi₃O_2.5Se₂ based field effect transistors demonstrated mobility of 10 and 15 cm²V^–1s^–1, respectively. Moreover, photodetector based on Bi₃O_2.5Se₂ showed exceptional photoresponse characteristics, such as an ultrafast response time of 9 ms, an extraordinary responsivity of 28 A/W, and a remarkable detectivity of 5.7 × 10⁹ Jones. Last but not least, we elucidated the role of various defects in defining the quality of 2D p-type WSe₂. We levered high-purity van der waals (vdW) crystals, commonly used in mechanical exfoliation, as the precursor and developed a facile physical vapor deposition (PVD) method to grow high-purity monolayer 2D WSe₂ film. The as-prepared WSe₂ exhibited exceptional electrical performance with a record-high hole mobility of 112 cm²V^–1s^–1, rivaling the mechanical exfoliation technique and establishing a new benchmark for vapor deposition-synthesized WSe₂.