Crystal violet as CMOS-compatible alkali-free promoter for CVD growth of MoSe2 monolayers: Comparative surface analysis with alkali-based promoter

The wafer-level growth of transition metal dichalcogenides (TMDs) using chemical vapor deposition (CVD) is essential for industrial applications involving complementary metal-oxide-semiconductor (CMOS) processes. In the CVD processes of TMDs, promoters containing alkali elements such as Na and K are typically used to obtain high-quality crystals. However, the use of alkali elements is rigorously restricted in CMOS processes because of contamination problems. In this study, we investigated crystal violet (CV) as a promising alkali-free promoter in the CVD growth of MoSe2. Particularly, the surface properties were intensively examined by optical, chemical, and topographical analyses and compared to those of samples prepared with NaOH as a representative alkalibased promoter. Na residues causing a doping effect were observed in the NaOH process, whereas the doping effect was negligible in the CV process. After the transfer process from the as-grown state, the strain effect in the NaOH process was prominently changed, resulting in wrinkles on MoSe2, whereas the wrinkles were negligible in the CV process, suggesting relatively smaller strain accumulation in the CV process during crystal growth. Our results showed the feasibility of CV as an alkali-free promoter for utilizing CVD-grown TMDs in industrial CMOS processes.