Crystallinity and Sub-Band Gap Absorption of Femtosecond-Laser Hyperdoped Silicon Formed in Different N-Containing Gas Mixtures

Femtosecond (fs)-laser hyperdoped silicon has aroused great interest for applications in infrared photodetectors due to its special properties. Crystallinity and optical absorption influenced by co-hyperdoped nitrogen in surface microstructured silicon, prepared by fs-laser irradiation in gas mixture of SF(6)/NF(3) and SF(6)/N(2) were investigated. In both gas mixtures, nitrogen and sulfur were incorporated at average concentrations above 10(19) atoms/cm(3) in the 20–400 nm surface layer. Different crystallinity and optical absorption properties were observed for samples microstructured in the two gas mixtures. For samples prepared in SF(6)/N(2), crystallinity and light absorption properties were similar to samples formed in SF(6). Significant differences were observed amongst samples formed in SF(6)/NF(3), which possess higher crystallinity and strong sub-band gap absorption. The differing crystallinity and light absorption rates between the two types of nitrogen co-hyperdoped silicon were attributed to different nitrogen configurations in the doped layer. This was induced by fs-laser irradiating silicon in the two N-containing gas mixtures.