Interband Transitions and Phonon Spectra of Si-Doped B12P2

✍ Scribed by H. Werheit; U. Kuhlmann; K. Shirai; Y. Kumashiro

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 254 KB
• Volume: 133
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7332

✦ Synopsis

Optical absorption and FT Raman spectra of polycrystalline B 12 P 2 prepared by CVD on silicon substrates are presented. The silicon content is rather high, and we assume that a ternary compound with the structure formula B 12 (P 2 ) 1!x (Si 2 ) x is formed. The absorption edge yields indirectly allowed transitions at 1.62, 1.80, 2.17, 2.46, and 2.75 eV, the energies of which are considerably lower than those reported by G. A. Slack et al. (1983, J. Phys. Chem. Solids 44, 1009) for pure B 12 P 2 . Six gap-state related transitions have ionization energies, which agree with those of electron traps in -rhombohedral boron. The number of one-phonon resonance frequencies agrees exactly with that predicted from group theory. The two-phonon spectra are quantitatively determined. Strong luminescence radiation superimposes the FT Raman spectrum, which differs qualitatively from that traditionally measured. This difference is explained by fluctuating distortions of the icosahedra related to the strong optical excitation of trapped electrons.