# Recent Advances in Black Silicon Surface Modification for Enhanced Light Trapping in Photodetectors
## 4 Black Silicon for Light Trapping in Photodetectors
The BSi/Ag NPs architecture was synthesized employing a wet chemical etching process. The responsivity values of the BSi/Ag NPs photodetector demonstrated  
Figure 6: (**a**) Absorptance spectra as a function of wavelength spanning from 250 nm to 2500 nm and (**b**) reflectance spectra as a function of wavelength over the same range, specifically for S-doped BSi in both annealed and nonannealed states, in addition to a comparison with an undoped BSi photodetector and an unprocessed Si device [75]. a considerable enhancement in comparison to those of a planar-Si/Ag thin-film Schottky photodetector, achieving responsivities of 0.277 mA/W and 0.226 mA/W at a reverse bias voltage of 3 V under 1319 nm and 1550 nm light irradiation, respectively. The Si-based photodetectors possess high detectivity and compatibility but are constrained by their low responsivity and abrupt decay when exposed to sub-bandgap wavelengths. The application of rapid thermal annealing and hydrogenated surface passivation methodologies has been observed to augment the responsivity across extensive bandgap ranges while improving the signal-to-noise ratio of photodetectors. The photodetector exhibits a sub-bandgap responsivity of 0.80 A/W at a voltage of less than 20 V for a wavelength of 1550 nm and an outstanding responsivity of 1097.60 A/W for a wavelength of 1080 nm. These characteristics underscore its potential competitiveness in fields such as infrared light detection, night vision imaging, and fiber-optic communication [78]. A recent study examined broadband BSi-based photodetectors characterized by high comprehensive properties and significant spectral responsivity [79]. These devices demonstrate responsiveness to incident light ranging from 400 nm to 1550 nm, as illustrated in Figure 7, and exhibit a notable responsivity of 40.59 A/W at 950 nm under a bias of \(-\)5 V. The produced photodetector reveals a consistent sub-bandgap photocurrent at 1550 nm. The hyper-doping of titanium (Ti) within Si enhances its efficacy, providing valuable implications for optical applications such as the detection of weak and infrared photons. The importance of photodetectors in various technologies, such as optical communication devices and sensors, cannot be overstated. However, the limitations of Si-based photodetectors hinder their light-detection capabilities, which is where BSi comes in as a groundbreaking solution. The microscopically textured surface of BSi plays a crucial role in enhancing its light-trapping capabilities, allowing BSi-based photodetectors to achieve improved light absorption and overall performance. By implementing BSi in the photodetector, significant improvements have been achieved, including high peak photoresponsivity, reduced current leakage, enhanced photocurrent rate, and remarkable EQE value. Additionally, photodetectors based on BSi exhibit enhanced sub-bandgap absorptance, reduced ionized electron concentration, and fast millisecond rise and delay times. Furthermore, BSi-based photodetectors address key challenges faced by photodetector devices, including low responsivity and abrupt decay when exposed to sub-bandgap wavelengths. This objective is accomplished through the application of rapid thermal annealing and hydrogenated surface passivation techniques in conjunction with BSi, which collectively enhance broadband spectral responsivity, yield high gain, and improve the signal-to-noise ratio of the photodetectors. Table 2 illustrates a concise overview of the recent BSi-based photodetectors to achieve enhanced functionalities and address the existing limitations of these optical devices.