Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe₂

Defects formed during chemical vapor deposition (CVD) of two-dimensional (2D) transition metal dichalcogenides (TMDs) currently limit their quality and optoelectronic properties. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed to enable next generation optoelectronic devices. In this work, isoelectronic doping is presented as a new strategy to form stable alloys and suppress defects and enhance photoluminescence (PL) in CVD-grown TMD monolayers. The isoelectronic substitution of W atoms for Mo atoms in CVD-grown monolayers of Mo_{1– x} W _x Se₂ (0 < x < 0.18) is shown to effectively suppress Se vacancy concentration by 50% compared to those found in pristine MoSe₂ monolayers, resulting in a decrease in defect-mediated nonradiative recombination, ≈10 times more intense PL, and an increase in the carrier lifetime by a factor of 3. Theoretical predictions reveal that isoelectronic W alloying to form Mo_{1– x} W _x Se₂ monolayers raises the energy of deep level defects in MoSe₂ to enable faster quenching, which is confirmed by low temperature (4–125 K) PL from defect-related localized states. Isoelectronic substitution therefore appears to be a promising synthetic method to control the heterogeneity of 2D TMDs to realize the scalable production of high performance optoelectronic and electronic devices.