# Recent Advances in Photodetectors Based on Two-Dimensional Material/Si Heterojunctions
## 3 Photodetectors Based on 2D Material-Si Heterojunctions
### NMD-Si Heterojunctions
The rectification behavior of the photodiode could be controlled by adjusting the gate voltage, resulting in a maximum rectification ratio of 1.0 \(\times\) 10\({}^{5}\). When exposed to light illumination, the photodiode exhibited exceptional detection performance, including a substantial open-circuit voltage of 0.6 V, a rapid response speed of 17.3 us and a broadband spectral response ranging from 400 to 1200 nm. In another study, the research same research group investigated the photodetection capability of an n-type PtS\({}_{2}\) nanoflake/p-type Si photodiode [124]. To enhance light absorption, the Si substrate was modified with a layer of Si pyramid microstructures Figure 6a. This device demonstrated a robust photovoltaic response to incident light, yielding a significant open-circuit voltage of 0.45 V at a light intensity of 70.32 mW/cm\({}^{2}\) at 500 nm. Consequently, the device functioned as a self-powdered detector, boasting a high photoresponsivity of 11.88 A/W. and reduced reverse current. Moreover, the addition of the graphene layer also enhanced the photoresponse, resulting in an increased short-circuit current and an open-circuit voltage. In order to enhance the IR response, black phosphorus (BP) QDs were dispersed on the surface of a PdSe\({}_{2}\)/Si heterojunction, as schematically shown in Figure 6f [131]. The introduction of BP QDs significantly improved the photodetection performance across the entire measured spectral range. The enhanced photoresponse in the middle IR range was attributed to the defects in the BP QDs, which were able to absorb IR light and generate a photocurrent. [PERSON] et al. discovered that the dark current could be greatly reduced by adding an ultrathin layer of SiO\({}_{2}\) between PtSe\({}_{2}\) and Si [60]. This additional interfacial layer not only reduced both forward and reverse currents but also improved the rectification ratio of the photodiode compared to devices without an SiO\({}_{2}\) layer. Additionally, the ideal factor of the photodiode was 1.015, which is close to the ideal value of 1, indicating low interfacial recombination in the PtSe\({}_{2}\)/ultrathin SiO\({}_{2}\)/Si heterojunction. Therefore, the photodiode exhibited excellent photodetection performance, including a high responsivity of 8.06 A/W, a high specific detectivity of 4.78 \(\times\) 10\({}^{13}\) Jones and an exceptional photo switch ON/OFF ratio of 1.29 \(\times\) 10\({}^{9}\) at zero bias at a wavelength of 808 nm. Furthermore, the responsivity at 1550 nm reached as high as 0.62 mA/W. For better comparison and understanding of the NMD/Si heterojunction photodetectors, the performance parameters of some typical devices are listed in Table 3.  
Figure 6: NMD/Si heterojunction photodetectors. (**a**) Schematic of the PtS\({}_{2}\)/pyramid Si heterojunction. Reproduced with permission from ref. [124]. Copyright 2022, American Chemical Society. (**b**) Schematic of the PtSe\({}_{2}\)/Si heterojunction. Reproduced with permission from ref. [125]. Copyright 2018, American Chemical Society. (**c**) Schematic of the PtSe\({}_{2}\)/SiNWA heterojunction. Reproduced with permission from ref. [126]. Copyright 2018, Nature Publishing Group. (**d**) Schematic of the PdSe\({}_{2}\)/pyramid Si heterojunction. Reproduced with permission from ref. [129]. Copyright 2019, WILEY-VCH. (**e**) Schematic of the PtTe\({}_{2}\)/Si Schottky junction with a graphene top electrode. Reproduced with permission from ref. [130]. Copyright 2020, WILEY-VCH. (**f**) Schematic of the BP QDs-PdSe\({}_{2}\)/Si heterojunction. Reproduced with permission from ref.