Au-Doped Black Silicon\nPhotodetector Fabricated by\na Femtosecond Laser with Excellent Near-Infrared Response

Silicon photonic devices are key components in optical\nimaging\nand sensing for communication, and the development of silicon-based\nphotodetectors with ideal performance in the visible and infrared\nspectral ranges can promote the application of silicon photonics in\nvarious photoelectronic systems. Here, a Au-doped black silicon photodetector\nwas prepared by a femtosecond laser direct writing technique. The\nconical micro-/nanostructures with different sizes were produced by\ndifferent laser fluence irradiation. Ultrafast pump–probe technology\nrevealed that the strong spallation process and phase explosion between\nAu and silicon facilitate the interfusion of Au atoms into the silicon\nlattice. EDS analyses, Raman spectra, and XPS spectra show the uniform\ndistribution of Au elements, multiconfiguration amorphous phase transition,\nand stable chemical valence states of Au elements in Au-doped black\nsilicon layers, respectively. The excellent geometric light trapping\nperformance of the surface conic structure-assisted photodetector\nachieved a high absorptance of 95% in the 200–1100 nm band.\nSimultaneously, the introduction of the intermediate band by Au hyperdoping\nalso leads to a strong absorptance of 75% in the 1100–2500\nnm band. The photoelectrical response rate of the Au-doped black silicon\nphotodetectors increased by 10 times in the infrared wavelength band\nby means of the introduced intermediate energy levels through Au element\ndoping. The switching photocurrent ratio is also found to be boosted\n10 times, which comes from the reduction of the photon injection barrier.\nThe excellent photoelectronic properties lead to the increased potential\nof femtosecond laser processing for integration with photonics and\nelectronics, which shows great possibilities in the further progress\nof energy devices, information technology, and artificial intelligence.