Silicon nanowires array capped with two shells as light-absorption antenna for self-driven broadband photodetectors

Silicon (Si) is one of the most important semiconductor materials, and Si in nanoscale has a direct bandgap; therefore, it can overcome the issues of poor light absorption for its bulk counterpart [Lu et al., Appl. Phys. Lett. 91, 263107 (2007)]. Currently, much interest is focusing on Si nanowires array (Si-NWA) for its unique characteristics, such as the enhanced light absorption and the superior electronic mobility, for photodetectors and solar cells [Ko et al., Mater. Sci. Semicond. Process. 33, 154–160 (2015) and Xie et al., ACS Nano 8, 4015–4022 (2014)]. Si-NWA or pyramid Si based photodetectors usually show higher performance than those based on the Si wafer due to the enhanced light absorption and the radial heterojunction [Coskun et al., Physica B 604, 412669 (2021) and Xiao et al., Adv. Mater. 30, 1801729 (2018)]. However, the light absorption spectrum of Si-NWA is limited within the near-infrared region, and its surface defects reduce the carriers' lifetime.