Femtosecond laser-structured silicon: properties and structure

Presentation Date: 

Tuesday, July 23, 2002

Location: 

Gordon Conference on Laser Interactions With Materials (Andover, NH)

Presentation Slides: 

Silicon surfaces that are microstructured with femtosecond laser pulses in a sulfur hexafluoride environment exhibit several remarkable properties, including near-unity below-band gap optical absorption (C. Wu et al., Appl. Phys. Lett. 78, 1850 (2001)). We report new structural and chemical characterization of this material, including cross-sectional TEM images of the microstructures. Our results indicate that the below-band gap absorption most likely comes from a surface layer of polycrystalline silicon roughly 1 micrometer thick, which includes nanopores, nanocrystals, and a high concentration of sulfur and fluorine impurities. This surface layer is observed both on deep conical microstructures formed with a large number of laser pulses and on very shallow, ridgelike microstructures formed with few laser pulses.