## 5 Conclusions  
In this work an overview on the NIR all-Si photodetectors has been presented. First, we have attempted to elucidate the most utilized physical effects allowing Si absorption at sub band-gap wavelength such as: mid-bandgap absorption, surface state absorption, internal photoemission absorption and two photon absorption. Then a quantitative comparison of the photodetectors proposed in the scientific literature based on the aforementioned absorption mechanisms, including both bulk and integrated devices, have been reviewed and summarized in Table 1. Overall, MBA based waveguide photodetectors seem to show the best performances if compared to devices based on others absorption mechanisms. In recent years a drastic reduction of the NIR all-Si photodetector size has been the most urgent task to reach, for this reason new structures such as MBA and SSA based ring resonator photodetectors and TPA based photonic crystal nanocavity photodetectors, have been fabricated. The scaling down of the devices, however, is still in progress and new perspectives have been opened by the surface plasmon polaritons (SPP) and its demonstrated capability to guide electromagnetic energy below the diffraction limit. It is our opinion that IPA based photodetectors associated to plasmonic waveguiding structures could play a key role in the future of the NIR all-Si photodetection and could be the new frontier in the field of low-cost silicon photonics. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Responsivity** & **Dark/leakage current** & **Bandwidth** & **Dimension** & **Effect** & **Type** & **Ref.** \\ \hline
8 mA/W & \(\sim 3\) nA & - & 10 mm & & \\ (\(\lambda\)- 1,550 nm V\({}_{\rm bias}\) = \(-1\) V) & (V\({}_{\rm bias}\) = \(-1\) V) & (waveguide length) & & \\
64 mA/W & 0.1 nA & - & 1.7 cm & & \\ (\(\lambda\)- 1,440 nm V\({}_{\rm bias}\) = \(-20\) V) & (V\({}_{\rm bias}\) = \(-20\) V) & (waveguide length) & Helium ion implantation & & \\  & & & 0,11 μm\({}^{2}\) & & \\
0.5 – 0.8 A/W & 2,5 nA/mm & 10–20 GHz & (cross section) & & \\ (\(\lambda\)- 1,550 nm V\({}_{\rm bias}\) = \(-5\) V) & (Vbias = \(-5\) V) & Waveguide length on the order of mm & & \\
0.1A/W & 0.1 nA & 7 GHz & 15 μm & & \\ (\(\lambda\)- 1,549 nm V\({}_{\rm bias}\) = \(-2\) V) & (Vbias = \(-2\) V) & (radius of ring resonator) & Si’ implantation ring resonator & & \\
50 mA/W & & & & & \\ (\(\lambda\) = 1,330 nm V\({}_{\rm bias}\) = \(-0.5\) V) & 120 \(\mu\)A/cm\({}^{2}\) & & 5 mm\({}^{2}\) & & \\
35 mA/W & (Vbias = \(-0.5\) V) & - & (active area) & Laser irradiation in presence of SF\({}_{6}\) & & \\
30 & & & & & \\
36 mA/W & 0.12 \(\mu\)A & - & 500 nm \(\times\) 100 nm & & \\ (\(\lambda\) = 1,575 nm V\({}_{\rm bias}\) = \(-11\) V) & (V\({}_{\rm bias}\) = \(-11\) V) & - & (cross section) & & \\
0.25 mA/W & 2.5 nA & - & - & & \\ (\(\lambda\) = 1,541.5 nm V\({}_{\rm bias}\) = \(-15\) V) & (V\({}_{\rm bias}\) = \(-15\) V) & - & - & \\
6 mA/W & 15 pA & - & - & & \\ (Around \(\lambda\) = 1,550 nm V\({}_{\rm bias}\) = \(-3\) V) & (Vbias = \(-3\) V) & - & - & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Performance summarization of NIR all-silicon photodetectors reported in the literature.