# Recent Advances in Photodetectors Based on Two-Dimensional Material/Si Heterojunctions
## 3 Photodetectors Based on 2D Material-Si Heterojunctions
### NMD-Si Heterojunctions  
Recently, NMD have attracted considerable attention due to their exceptional electrical and optoelectronic properties. For instance, a phototransistor based on few-layer PtS\({}_{2}\) demonstrated a remarkably high photoresponsivity of 1.56 \(\times\) 10\({}^{3}\) A/W [119]. PtSe\({}_{2}\), on the other hand, displayed a thickness-dependent metal-to-semiconductor transformation [120]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Materials** & **Measurement** & **R/A-W\({}^{-1}\)** & **D\({}^{\prime}\)/Jones** & **EQE** & \multicolumn{2}{c}{**Time**} & **Ref.** \\  & **Conditions** & **R/A-W\({}^{-1}\)** & **D\({}^{\prime}\)/Jones** & **EQE** & \multicolumn{2}{c}{**(Rise/Down)**} & **Ref.** \\ \hline MoS\({}_{2}\)/Si & 808 nm/\(-\)2 V & 0.07 & & & & [62] \\ WS\({}_{2}\)/Si & 660 nm/\(-\)5 V & 5.7 & & & 670 μs/998 μs & [104] \\ MoS\({}_{2}\)/Si & 650 nm/\(-\)2 V & 11.9 & \(2.1\times 10^{10}\) & & 30.5 μs/71.6 μs & [106] \\ MoTe\({}_{2}\)/Si & 980 nm/0 V & 0.19 & \(6.8\times 10^{13}\) & 24\% & 150 μs/380 ns & [107] \\ MoTe\({}_{2}\)/Si & 700 nm/0 V & 0.26 & \(2\times 10^{13}\) & & 5 μs/8 ns & [108] \\ MoSe\({}_{2}\)/Si & 980 nm/0 V & 0.7205 & \(10^{13}\) & 91\% & 13 μs/35 μs & [109] \\ MoSe\({}_{2}\)/Si & 808 nm/0 V & 0.3 & \(10^{13}\) & & 3 μs/40 μs & [111] \\ WS\({}_{2}\)/Si & 365 nm/0 V & 0.004 & \(1.5\times 10^{10}\) & & 1.1 μs & [112] \\ MoSe\({}_{2}\)/Si & 808 nm/\(-\)2 V & 0.908 & \(1889\times 10^{13}\) & & 56 ns/825 ns & [114] \\ MoSe\({}_{2}\)/Si & 550 nm/5 V & 9 & \(10^{14}\) & & 9 μs/7 μs & [115] \\ RCO-MoS\({}_{2}\)/Pyramid Si & 808 nm/0 V & 21.8 & \(3.8\times 10^{15}\) & & 2.8 μs/46.6 μs & [58] \\ WS\({}_{2}\)/Pyramidal Si & 980 nm/0 V & 0.29 & \(2.6\times 10^{14}\) & & 5.2 μs/22.3 μs & [116] \\ 1T\({}^{-}\)MoTe\({}_{2}\)/Si & 980 nm/0 V & 0.526 & \(2.17\times 10^{12}\) & & 1.9 μs/41.5 μs & [49] \\ WS\({}_{2}\)/WSe\({}_{2}\)/Si & 405 nm/1.5 V & 3.72 & \(2.39\times 10^{12}\) & 1140\% & 8.47 ms/7.98 ms & [117] \\ MoS\({}_{2}\)/Si & 850 nm/6 V & 0.01007 & \(4.53\times 10^{10}\) & & 78 μs/76 μs & [118] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of properties of TMD/silicon heterojunction devices. Figure 5: Schematic and photodetection performance of TMD/Si heterojunction devices. (**a**) Schematic of WS\({}_{2}\)/Si heterojunction. Reproduced with permission from ref. [104]. Copyright 2016, American Chemical Society. (**b**) Spectral response of MoTe\({}_{2}\)/Si heterojunction photodetector. Reproduced with permission from ref. [107]. Copyright 2020, WILEY-VCH. (**c**) Scanning electron microscopy image of vertical aligned MoS\({}_{2}\) nanosheets. Reproduced with permission from ref. [113]. Copyright 2017, WILEY-VCH. (**d**) Schematic of the RGO-MoS\({}_{2}\)/Pyramid Si heterojunction photodetector. Reproduced with permission from ref. [58]. Copyright 2018, WILEY-VCH. (**e**) Current–voltage curves with and without light illumination for a 1T\({}^{-}\)MoTe\({}_{2}\)/Si heterojunction photodetector. (**f**) Spectral response and specific detectivity of a 1T\({}^{-}\)MoTe\({}_{2}\)/Si heterojunction photodetector. Reproduced with permission from ref. [49]. Copyright 2023, Nature Publishing group. When bilayer PtSe\({}_{2}\) was combined with defect modulation, it exhibited strong light absorption in the mid-IR region and showed excellent photodetection performance [121]. Experimental results indicated that the few-layer PdSe\({}_{2}\) achieved an impressive field effect mobility of 210 cm\({}^{2}\)/Vs [122]. The exceptional properties exhibited by these materials make them highly attractive for various photodetection applications. [PERSON] et al. employed mechanically exfoliated multilayer n-type PdSe\({}_{2}\) nanoflakes to fabricate PdSe\({}_{2}\)/Si p-n photodiodes [123]. This was achieved by transferring the PdSe\({}_{2}\) nanoflakes onto the surface of a p-type Si substrate. To modulate the conductance of the PdSe\({}_{2}\) nanoflake in the diode, an ionic liquid gate was utilized.