# Recent Advances in Black Silicon Surface Modification for Enhanced Light Trapping in Photodetectors
## 4 Black Silicon for Light Trapping in Photodetectors
The device exhibited significant photo-responsivities across the visible to MIR spectrum region (405 nm to 4 \(\upmu\)m),  
Figure 4: (**a**) Spectral responsivity of the BSi-based photodetector versus wavelength in visible and NIR regions as a function of varied temperatures from 10 K to 300 K; (**b**) the relationship between peak responsivity and detectivity in relation to temperature for the sulfur-hyper-doped BSi-based photodetector [70]. Figure 5: (**a**) Dark current features of the BSi\(-\)based photodetectors having lateral heterojunction (red line) and two vertical heterojunctions (Mesa and sandwich structures); (**b**) dark current (red line) and photocurrent (blue line) merit for the BSi\(-\)based photodetector fabricated in lateral heterojunction structure; inset presents the schematic diagram of the corresponding lateral structure of the BSi photodetector [71]. attributed to the high light absorption properties of BAs and the effective optical coupling capabilities of the SOI substrate. [PERSON] et al. demonstrated the utilization of chromium (Cr)-hyper-doped BSi material in Si-based infrared photodetectors, exhibiting enhanced sub-bandgap absorptance and reduced ionized electron concentration [74]. The Cr-hyper-doped BSi enabled the development of BSi photodiodes with a face-to-face configuration, achieving a significant responsivity of 0.57 A/W at 1.31 \(\upmu\)m wavelength and fast millisecond rise and delay times. Furthermore, [PERSON] et al. showcased the exceptional photosensitivity properties of MSM infrared photodetectors fabricated from S-doped BSi [75]. As illustrated in Figure 6, these photodetectors demonstrated an exceptional responsivity of 367 mA/W at a voltage of 10 V, accompanied by rising and falling times of 53.82 ms and 64.51 ms, respectively, when subjected to 1030 nm laser illumination. This performance notably exceeds unprocessed Si, which exhibited a responsivity of 47 mA/W at the same voltage and under analogous experimental conditions. Furthermore, photodetectors made of two-dimensional materials (2 DM PDs) can satisfy the urgent requirements of Si photonics for cost-effective, high-performance, and wide-spectrum photodetection. In Figure 6, the absorbance refers specifically to the S-doped black silicon (BSi) surface, which was processed using femtosecond laser ablation. The measurement was taken to demonstrate the intrinsic light-absorbing properties of the S-doped BSi surface, particularly in the visible to near-infrared (0.2-2.5 \(\upmu\)m) spectrum. The data represent the effectiveness of the nanostructured BSi in minimizing light reflection while maximizing absorption across a wide range of wavelengths. The creation of micro/nanostructures on the BSi surface, formed through laser ablation, is responsible for the reduction in reflectance and enhanced absorption. These structures scatter and trap incoming light, increasing the optical path length and minimizing transmission losses. This distinction is crucial, as it highlights the performance of the S-doped BSi surface alone, without any external coatings or materials influencing the absorbance measurements. This allows for a direct comparison of the intrinsic light-trapping efficiency of the BSi nanostructures, which is key to its application in high-performance photodetectors and other optical devices that rely on efficient light absorption [72]. [PERSON] et al. demonstrated advancements in developing Si/2 DM PDs operating within the NIR to MIR wavelength range, rendering them appealing for numerous applications [76]. The use of sub-bandgap NIR Si photodetectors is essential in the domain of integrated Si photonics. In an investigation conducted by [PERSON] et al., BSi-based photodetector was successfully developed utilizing a BSi/Ag NPs Schottky junction [77]. This photodetector proficiently captures sub-bandgap light and produces a photocurrent via an amalgamation of inner photoemission, optical confinement, and surface plasmon-enhanced absorption.