Optical Blocking Layer and Field-Induced Junction on Silicon Nanowire Multispectral Photodetectors Toward High Quantum Efficiency

Crystalline silicon nanowires (c-SiNWs) have unique optical characteristics that enable tuning of their spectral response depending on their diameter. However, real-world applications of c-SiNWs multispectral photodetectors are still hampered by their low selectivity and low quantum efficiency (< 30%). The primary obstacles include the broad-spectrum light absorption of the bottom crystalline silicon (c-Si) substrate underneath the c-SiNWs. In addition, it is difficult to form appropriate p-n junctions on c-SiNWs and it leads to severe recombination which makes low external quantum efficiency (EQE). In this study, a thin metal film was applied as an optical blocking layer to block light absorption in the bottom c-Si substrate, and atomic layer deposition (ALD)-based Al₂O₃ was employed to form a dopant-free p-n junction on diameter-controlled c-SiNWs. Consequently, the maximum EQE of the fabricated photodetector was 77.4% at 620 nm with remarkable wavelength selectivity. This work removes major stumbling blocks for the use of c-SiNW as selective light spectral bandpass photodetectors.