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

Haibin Sun; Jiamin Xiao; Suwan Zhu; Yue Hu; Guojin Feng; Jun Zhuang; Li Zhao

doi:10.3390/ma10040351

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

Materials (Basel). 2017 Mar 28;10(4):351. doi: 10.3390/ma10040351.

Authors

Haibin Sun¹, Jiamin Xiao², Suwan Zhu³, Yue Hu⁴, Guojin Feng⁵, Jun Zhuang⁶, Li Zhao⁷

Affiliations

¹ Collaborative Innovation Center of Advanced Microstructures, State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China. sunhaibin007@gmail.com.
² Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. 12110190077@fudan.edu.cn.
³ Collaborative Innovation Center of Advanced Microstructures, State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China. 14110190075@fudan.edu.cn.
⁴ Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. 14110720002@fudan.edu.cn.
⁵ Spectrophotometry Laboratory, National Institute of Metrology, Beijing 100013, China. fengguojin@nim.ac.cn.
⁶ Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. junzhuang@fudan.edu.cn.
⁷ Collaborative Innovation Center of Advanced Microstructures, State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China. lizhao@fudan.edu.cn.

Abstract

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 SF₆/NF₃ and SF₆/N₂ were investigated. In both gas mixtures, nitrogen and sulfur were incorporated at average concentrations above 10¹⁹ atoms/cm³ 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 SF₆/N₂, crystallinity and light absorption properties were similar to samples formed in SF₆. Significant differences were observed amongst samples formed in SF₆/NF₃, 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.

Keywords: crystallinity; femtosecond laser; hyperdoped; nitrogen; sub-band gap absorption.