The Study Of Fabrication And Optical Properties Of Femtosecond Laser Induceed Micro/Nano-Structures On Silicon Surface

With femtosecond laser processing of silicon, the surface will form a layer of micro/nano-structures with conical shape, because of these structures the optical properties of silicon will totally change, it has strong light absorption for ultra-broad spectral, we called this new material for “black silicon”. This micro-structured surface can be widely used in optical detectors, solar cells, field emission devices, etc. These new properties of black silicon is related to the morphology of micro/nano-structures. In this thesis we mainly study the influence of different laser energy deposition models and different laser wavelength to the micro/nano-structures induced by femtosecond laser.We experimentally investigate the average scale of structures change with different laser energy deposition methods. The results of experiment show that even when we use same laser energy to fabricate micro/nano-structures on silicon surface, the morphology of the surface can be different. Excessive pulse number or overtop laser power is no use to structure growth, there is a optimal laser energy deposition method, at this condition we can use less time and laser energy to get the optimal structure. We create a physical model to present silicon surface morphology process.We also test the light absorption efficiency of the best sample from my experiment, the result shows it has a very good light absorption of the wavelength from 250 nm to 2500 nm.Furthermore, we experimentally investigate the differences between two micro/nano-structures fabricated by 800 nm and 400 nm femtosecond laser. Because of the penetration depth of laser pulse increase with the increase wavelength, 400 nm laser need less energy to fabricate complete structure, but if laser energy is enough the structure induced by 800 nm laser is much bigger than 400 nm laser.