# Recent Advances in Black Silicon Surface Modification for Enhanced Light Trapping in Photodetectors
###### Abstract  
The intricate nanostructured surface of black silicon (BSi) has advanced photodetector technology by enhancing light absorption. Herein, we delve into the latest advancements in BSi surface modification techniques, specifically focusing on their profound impact on light trapping and resultant photodetector performance improvement. Established methods such as metal-assisted chemical etching, electrochemical etching, reactive ion etching, plasma etching, and laser ablation are comprehensively analyzed, delving into their mechanisms and highlighting their respective advantages and limitations. We also explore the impact of BSi on the emerging applications in silicon (Si)-based photodetectors, showcasing their potential for pushing the boundaries of light-trapping efficiency. Throughout this review, we critically evaluate the trade-offs between fabrication complexity and performance enhancement, providing valuable insights for future development in this rapidly evolving field. This knowledge on the BSi surface modification and its applications in photodetectors can play a crucial role in future implementations to substantially boost light trapping and the performance of Si-based optical detection devices consequently. black silicon; surface modification; light trapping; photodetectors; nanostructures; etching; laser ablation +
Footnote †: journal: Applied Sciences  
morphology and roughness [13]. Coating the surfaces with thin films or chemical and physical etching are techniques to change the morphology of the surface and roughness of the material; at the same time, these two ways can also be used to have an antireflection coating or an antireflection structure [14]. With this in mind, the antireflection structures have also shown resistance to destruction from high-energy lasers of nearly 60 J/cm\({}^{2}\)[15]. However, unique properties of the material can be obtained by exercising control over the parameters of the etching methods [16]. The etching methods can be classified into two divisions: wet etching (chemical methods) and dry etching (combined physical and chemical methods). Wet and dry etching as well as laser ablation methods are widely adopted for processing nanoscale features on Si samples, which can dramatically elevate light trapping for Si-based photodetectors, paving the way for improved efficiency [17; 18]. The nanoscale features on BSi, including porous structures and needle-like protrusions, effectively enhance the optical properties by trapping the incident light through light scattering and multiple internal reflections, thus minimizing surface reflectance and approaching near-perfect absorption across a broad spectral range [19; 20; 21]. Through the etching process and by leveraging the exceptional light trapping capabilities of BSi, a surface engineered by [PERSON] et al. through RIE achieved record-low reflectance (~1.1%) across a broad spectral range exceeding 2500 nm. This optimized BSi structure holds significant promise for photothermal applications, including imaging, desalination, and beyond [22]. By laser ablation, particularly with nanosecond pulsed laser ablation, [PERSON] et al. successfully tailored Se-doped BSi with remarkable broadband light absorption in the range spanning 400-2200 nm, exceeding 96.81% before annealing and 81.28% after 600 \({}^{\circ}\)C annealing. This near infrared (NIR)-enhanced BSi, subsequently integrated into double four-quadrant photodetectors, exhibited exceptional performance metrics with elevation in the responsiveness, a decrease in the dark current, quick response times, and the slightest crosstalk, paving the way for its application in demanding fields like night vision detection and medical imaging [23]. In this work, we present an in-depth review of the recent efforts on the BSi chemical and physical processing, with a keen interest in leveraging the BSi structures for light trapping to improve the performance of photodetectors.