Field enhanced in-plane homostructure in a pure MoSe2 phototransistor for the efficient separation of photo-excited carriers
Two-dimensional transition-metal dichalcogenides (TMDs) have attracted significant attention, owing to their excellent electrical and optoelectrical properties, especially MoS2. However, the photoresponse of pure MoSe2 is still unsatisfactory due to the absence of a photoresponse enhancement mechanism, which impedes its rapid development in optoelectronics. Here, we report a pure MoSe2 phototransistor with an in-plane lateral thickness-dependent MoSe2 homojunction in the channel perpendicular to the charge transfer direction as an enhancement scheme for the first time. An in-plane lateral built-in field is spontaneously formed due to the different electrical band structure of MoSe2 with different thickness, which facilitates the efficient separation of photo-excited carriers. Furthermore, with an increase in the applied negative back-gate voltage, separation could be further strengthened due to the increase of the built-in field in the homojunction resulting in optimization of the photoresponse performance. These results suggest a facile approach for the enhancement of photoresponse performance to materials which possesses a thickness-dependent energy band structure.