Analysis of photoluminescence behavior of high-quality single-layer MoS₂

The ability to tailor and enhance photoluminescence (PL) behavior in two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS₂) is significant for pursuing optoelectronic applications. To achieve this, it has been essential to obtain high-quality single-layer MoS₂ and fully explore its intrinsic PL performance. Here, we fabricate single-layer MoS₂ by a thermal vapor sulfurization method in which a pre-deposited molybdenum trioxide (MoO₃) thin film is sulfurized over a short period (for several minutes) to turn into MoS₂. These as-grown MoS₂ crystals show quite strong PL, which is about one order of magnitude higher than that of chemical- vapor-deposited MoS₂. Temperature- and power-dependent spectroscopy measurements disclose the apparent influence of sulfur (S) vacancies on the PL behavior and the noticeable free-to-bound exciton recombinations in the luminescence process. The fact that PL intensity of the sample in vacuum sharply lowered down relative to in air reveals that the high PL is facilitated by molecular adsorption on S vacancies in air. And multi-channel decay processes coupled with S vacancies are revealed in the time-resolved PL spectroscopy. In our work, single-layer MoS₂ with high PL is synthesized and its defect-induced PL features are analyzed, which is of great importance for developing advanced nano-electronics and optoelectronics based on 2D structures.