  Two dimensional material/semiconductor heterostructures offer alternative
platforms for optoelectronic devices other than conventional Schottky and p-n
junction devices. Herein, we use MoS2/GaAs heterojunction as a self-driven
photodetector with wide response band width from ultraviolet to visible light,
which exhibits high sensitivity to the incident light of 635 nm with
responsivity as 446 mA/W and detectivity as 5.9*10^13 Jones (Jones = cm Hz1/2
W-1), respectively. Employing interface design by inserting h-BN and
photo-induced doping by covering Si quantum dots on the device, the
responsivity is increased to 419 mA/W for incident light of 635 nm. Distinctly,
attributing to the low dark current of the MoS2/h-BN/GaAs sandwich structure
based on the self-driven operation condition, the detectivity shows extremely
high value of 1.9*10^14 Jones for incident light of 635 nm, which is higher
than all the reported values of the MoS2 based photodetectors. Further
investigations reveal that the MoS2/GaAs based photodetectors have response
speed with the typical rise/fall time as 17/31 {\mu}s. The photodetectors are
stable while sealed with polymethyl methacrylate after storage in air for one
month. These results imply that monolayer MoS2/GaAs heterojunction may have
great potential for practical applications as high performance self-driven
photodetectors.
