Optical Absorption Properties Of The Micro Structure Of Silicon Metal Films

Arrays of sharp conical spikes can be formed on silicon surface by cumulative irradiation of ultrashort laser pulses in the presence of ambient gases, and the surface-microstructured silicon show remarkably enhanced light absorptance in a wide wavelength range. The microstructure's morphology depends not only on the shot number, fluence, and polarization of laser, but also the species, and the pressure of the ambient gas, etc. The plasma induced by femtosecond laser pulses irradiated on silicon surface has been investigated. The plasma emission spectra show strong dependence on the structuring ambient gas species and pressure. Among the four ambient gases (SF₆, N₂, air and vacuum), the plasma obtained in SF₆ shows the strongest signals. The emission intensities increase initially with the gas pressure, and achieve strongest at 70 kPa, then decreases as the pressure further increases. The plasma signals provide an insight into the reaction process, and the optimum gas pressure and species within our knowledge has been obtained, helping us to have a better understanding and a better choice of the experimental condition for the formation of the microstructures on silicon surface by femtosecond laser pulses irradiation.The light absorption, from 0.3 to 16.7 micrometer, of the surface-microstructured silicon and the coated metal film has been investigated. It shows significantly enhanced light absorption over such a wide wavelength range. The light absortance has a strong relationship with the ambient gas, the surface morphology, and the thickness of the silver film. The surface-microstructured silicon formed in SF₆ and N₂ has different surface morphology, resulting in different light absorption property. And the light absorption varies with the height and density of the spikes formed on silicon, which indicates that the surface microstructures play an important role in the enhancement of light absorption. The absorption of the metal film coated on microstructured silicon depends on the height and density of the spikes, and it decreases as the thickness of the silver film increases. These remarkable optical properties open up new possibilities for potential applications in optoelectronic and detector fields, such as infrared detectors, stealth technology, silicon solar cells, and so on.