Photogating of mono- and few-layer MoS₂

We describe a photogating effect in mono- and few-layer MoS₂, which allows the control of the charge carrier density by almost two orders of magnitude without electrical contacts. Our Raman studies are consistent with physisorbed environmental molecules, which effectively deplete the intrinsically n-doped charge carrier system via charge transfer and which can be gradually removed by the exposure to light. This photogating process is reversible and precisely tunable by the light intensity. The photogating efficiency is quantified by comparison with measurements on electrostatically gated MoS₂.