Optical band gap of semiconductive type II Si clathrate purified by centrifugation

• Published in: Journal of non-crystalline solids 2012-09, Vol.358 (17), p.2138-2140
• Main Authors: Himeno, Roto, Ohashi, Fumitaka, Kume, Tetsuji, Asai, Erika, Ban, Takayuki, Suzuki, Takatoshi, Iida, Tamio, Habuchi, Hitoe, Tsutsumi, Yasuo, Natsuhara, Hironori, Nonomura, Shuichi
• Format: Article
• Language: English
• Subjects: Amorphous semiconductors; glasses; Band gap; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Diffuse reflection spectroscopy; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Optical absorption; Optical materials; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Optics; Photonic bandgap materials; Physics; Si clathrate
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2011.12.064

The optical properties of Si clathrate, which is believed to have potential as a new Si-based material for optical devices, were investigated in this study. Si clathrates with type II structure (NaxSi136) with low Na content (x=1.3, 2.0) were synthesized by thermal decomposition of NaSi. The synthesized samples were purified by centrifugation using a solution of CH2Br2–C2Cl4 to remove impurities. Using the obtained high purity samples (Na1.3Si136, 93wt.%; Na2.0Si136, 90wt.%), the optical absorption spectra of NaxSi136 were clarified, for the first time, from diffuse reflection measurements. The inclusion of Na in Si136 was found to cause free carrier absorption in the infrared region but had little effect on the fundamental absorption edge found in the visible region. ► We synthesized Si clathrate NaxSi136 with x=1.3, 2.0. ► NaxSi136 was purified by centrifugation method. ► Diffuse reflection spectra were measured. ► A fundamental absorption edge was observed at 1.2–1.8eV. ► Strong free carrier absorption was detected below 1eV.