Enhancing the Optoelectronic Performance of MoSe₂ Nanosheets/Si Heterojunctions with Graphene Electrodes

A MoSe₂ nanosheet/Si heterojunction photodetector with a graphene electrode was fabricated via mechanical exfoliation. This work demonstrates that graphene significantly enhances carrier mobility within the MoSe₂ nanosheets, thereby facilitating efficient separation and transport of photogenerated carriers from the heterojunction interface to the top electrode. This mechanism consequently leads to a substantial improvement in overall device performance. The fabricated device demonstrates a rectification ratio of 1294.3 at room temperature. Under 650 nm red light illumination, it exhibits a responsivity (R) of 229.8 A/W, a specific detectivity (D^*) of 1.9 × 10¹² Jones, and an external quantum efficiency (EQE) of 4.5 × 10⁴%. Under 405 nm blue light illumination, it achieves an R of 201.9 A/W, a D^* of 1.7 × 10¹² Jones, and an EQE of 6.2 × 10⁴%. The device demonstrates broadband photodetection capability across the visible to near-infrared spectrum, featuring the fastest measured rise and fall times of 810 and 950 μs at 700 nm wavelength. Furthermore, temperature-dependent measurements reveal a significant impact on optoelectronic properties: At low temperatures, the photoresponse performance deteriorates due to the reduction of the effective barrier height within the device.