The hydrogenation of C-rich Si leads to the formation of two (almost) energetically degenerate H2*(C) complexes, each containing one substitutional C (Cs) and two interstitial H atoms which are located at a bond-centered (bc) and an antibonding (ab) site, respectively. The two defects are trigonal: Cs-Hbc Si-Hab and H ab-Cs Hbc-Si. Fourier-transform infrared (FTIR) absorption spectra of these two defects should show two Cs-H and two Si-H stretch modes, but the Hab-Cs mode was absent in earlier studies. The missing line has now been observed by FTIR in especially C rich Si material. The line is unexpectedly broad, suggesting a very short vibrational lifetime. Partial D substitutions result in the formation of a Hab-Cs Dbc-Si center. In this defect, the Hab-Cs line shifts by only 0.3cm-1 but becomes very sharp, suggesting a long lifetime. The IR line widths show that the vibrational lifetime of the Hab-Cs mode in H ab-Cs Dbc-Si is about 16 times longer than that of the same Hab-Cs mode in Hab-Cs Hbc-Si. This paper contains experimental data and first-principles calculations which explain this isotope effect.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Mar 13 2013|