Two-dimensional materials have been demonstrated as promising toolboxes for optoelectronics.Transition metal carbides and nitrides (MXenes),members of an emerging family of two-dimensional materials,have drawn extensive attention in optoelectronics owing to their excellent conductivity and tunable electronic properties.Herein,a photodetector based on the two-dimensional van der Waals heterostructure of Ti3C2Tx MXene and a MoS2 monolayer was constructed to observe the ambipolar photoresponse,which showed a positive photoresponse in the visible spectrum (500-700 nm) and a negative photoresponse at longer wavelengths (700-800 nm).The device exhibited a high negative responsivity of 1.9 A/W and a detectivity of 2.1 × 1010 Jones under 750 nm light illumination.Detailed experiments demonstrate that the negative photoresponse arises from the heterostructure-induced trap energy level,which confines the excited photoelectrons and leads to an inverse current.This work demonstrates a unique optoelectronic phenomenon in MoS2/MXene heterostructures and provides valuable insights into the development of new photodetection materials.