Electrostatic control of photoluminescence from A and B excitons in monolayer molybdenum disulfide.

Tailoring excitonic photoluminescence (PL) in molybdenum disulfide (MoS 2 ) is critical for its various applications. Although significant efforts have been devoted to enhancing the PL intensity of monolayer MoS 2 , simultaneous tailoring of emission from both A excitons and B excitons remains largely unexplored. Here, we demonstrate that both A-excitonic and B-excitonic PL of chemical vapor deposition (CVD)-grown monolayer MoS 2 can be tuned by electrostatic doping in air. Our results indicate that the B-excitonic PL changed in the opposite direction compared to A-excitonic PL when a gate voltage ( V g ) was applied, both in S-rich and Mo-rich monolayer MoS 2 . Through the combination of gas adsorption and electrostatic doping, a 12-fold enhancement of the PL intensity for A excitons in Mo-rich monolayer MoS 2 was achieved at V g = -40 V, and a 26-fold enhancement for the ratio of B/A excitonic PL was observed at V g = +40 V. Our results demonstrate not only the control of the conversion between A 0 and A - , but also the modulation of intravalley and intervalley conversion between A excitons and B excitons. With electrostatic electron doping, the population of B excitons can be promoted due to the enhanced intravalley and intervalley transition process through electron-phonon coupling. The electrostatic control of excitonic PL has potential applications in exciton physics and valleytronics involving the B excitons.