Abstract
Chemical vapor deposition (CVD) is one of the most promising, scalable synthetic techniques to enable large-area synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDs) for the realization of next generation optoelectronic devices. However, defects formed during the CVD growth process currently limit the quality and electronic properties of 2D TMDs. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed. In this work, isoelectrnic doping to produce stable alloy is presented as a new strategy to suppress defects and enhance photoluminescence (PL) in CVD-grown TMD monolayers. The random, isoelectronic substitution of W atoms for Mo atoms in CVD-grown monolayers of Mo1-xWxSe2 (0<x<0.18) is shown to effectively suppress Se vacancy concentration by 50% compared to those found in pristine MoSe2 monolayers. The resultant decrease in defect-medicated non-radiative recombination in the Mo0.82W0.18Se2 monolayers yielded ~10 times more intense PL and extended the carrier lifetime by a factor of 3 compared to pristine CVD-grown MoSe2 monolayers grown under similar conditions. Low temperatures (4−125 K) PL from defect-related localized states confirms theoretical predictions that isoelectronic W alloying should suppress deep levels in MoSe2, showing that the defect levels in Mo1-xWxSe2 monolayers are higher in energy and quenched more quickly than in MoSe2. 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.
