Enhanced photocurrent and photoluminescence spectra in MoS₂ under ionic liquid gating

We report substantial improvements and modulation in the photocurrent (PC) and photoluminescence (PL) spectra of monolayer MoS₂ recorded under electrostatic and ionic liquid gating conditions. The photocurrent and photoluminescence spectra show good agreement with a dominant peak at 1.85 eV. The magnitude of the photoluminescence can be increased 300% by ionic liquid gating due to the passivation of surface states and trapped charges that act as recombination centers. The photocurrent also doubles when passivated by the ionic liquid. Interestingly, a significant shift of the PL peak position is observed under electrostatic (14 meV) and ionic liquid (30 meV) gating, as a result of passivation. The ionic liquid provides significant screening without any externally applied voltage, indicating that these surface recombination centers have net charge. The acute sensitivity of monolayer MoS₂ to ionic liquid gating and passivation arises because of its high surface-to-volume ratio, which makes it especially sensitive to trapped charge and surface states. These results reveal that, in order for efficient optoelectronic devices to be made from monolayer MoS₂, some passivation strategy must be employed to mitigate the issues associated with surface recombination.