Multi-layered MoS2 phototransistors as high performance photovoltaic cells and self-powered photodetectors

Abstract

An optoelectronic diode based on a p–n junction is one of the most fundamental device building blocks with extensive applications. Compared with graphene, layered transition-metal dichalcogenides demonstrate promising applications in novel valley-electronics and opto-electronics. Here we reported the fabrication and optoelectronic properties of a single multilayer MoS₂ sheet. Our results indicate that the thin MoS₂ shows a linear transport property while thick MoS₂ shows diode characteristics with well-defined current rectification behavior. We assign that the rectification behavior is due to the formation of a p–n junction in the single multilayer MoS₂ piece. The intrinsic defects in MoS₂ can change the conduction polarity, such as: sulfur vacancies contribute to the n-type behavior while sulfur interstitials and molybdenum vacancies contribute to the p-type conduction. The variation of intrinsic defects and stoichiometry is obvious over the micrometer range in thick MoS₂. The fabricated MoS₂ transistors were assessed under bias and gate voltage modulation when exposed to red, green and UV light under vacuum. The multilayer MoS₂ shows dominant p-type behavior under dark conditions while its shows dominant n-type conduction under light illumination. In addition, this MoS₂ phototransistor shows an evident photovoltaic effect. The open-circuit voltage (V_oc) and short-circuit current (I_sc) are observed to be −0.48 V and 494 nA under red illumination. These results demonstrate the potential application of a single multilayer MoS₂ sheet in optoelectronics, such as light-emitting diodes (LEDs), field-effect photovoltaic cells and photodetectors.