INTERBAND-TRANSITIONS AND PHONON-SPECTRA OF SI-DOPED B12P2

Optical absorption and FT Raman spectra of polycrystalline B12P2 prepa red by CVD on silicon substrates are presented, The silicon content is rather high, and me 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 pare B12 P2. Six gap-state related transitions have ionization energies, which agree with those of electron traps in beta-rhombohedral boron, The num ber of one-phonon resonance frequencies agrees exactly with that predi cted from group theory, The two-phonon spectra are quantitatively dete rmined, Strong luminescence radiation superimposes the FT Raman spectr um, 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. (C) 199 7 Academic Press.