Hydrogen Molecules in Crystalline Silicon

The hydrogen (H2) molecule in silicon is not only interesting in its own right (Johnson and Herring, 1989) but also as a possible component in the formation and dissociation process of all H-related complexes. We focus in this section on theoretical studies of H2 molecules in crystalline silicon. 

One of the earliest studies was an MNDO-cluster treatment by Corbett et al. (1983) of the isolated interstitial hydrogen and the corresponding molecule. In this early study, the isolated H was found to be stable at the M-site in silicon. This is directly between two adjacent C-sites, where the C-site is directly between next-near-neighbor silicons. (We note that in these calculations, the C- and M-site energies are very similar.) It was not known at that time, however, that the BC site is the stable location for neutral isolated interstitial hydrogen (see Chapter 16). In the Corbett study, an H2 molecule was found to be stable (or at least, metastable) in the tetrahedral interstitial site when oriented along a (111) direction. The 

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We can compare the steady-state profiles discussed above to experiments. In Fig. 5 we see a profile from Widmer et al. [155] in amorphous silicon, suggestive of the steady-state profile for molecule formation. Molecule formation has also been indicated in experiments in crystalline silicon vdiere near surface concentrations much higher than the solubility have been foiind [51,57,156, 157]. We can also see data on the diffusion coefficient in Fig. 6, where the diffusion coefficient drops from the value for atomic hydrogen much as an effective diffusion coefficient would, but then does not continue to drop the interpretation of the latter trend is not clear. 

Raman and IR spectra were used to monitor the phase behaviour of solid H2 at pressures above 200 GPa and liquid helium temperatures. The Raman spectrum of H2 in crystalline silicon shows vHH at 4158 cm and a rotational band at 590 cm The Raman spectrum of float-zone crystalline silicon after exposure to a hydrogen plasma contained bands at 3601 and 2622 cm due to H2 and D2 molecules respectively, at a tetrahedral site within the silicon lattice. ... 

Silicon-backbone materials include silane oligomers, polysilanes, silicon clusters, and amorphous and crystalline silicons. These materials have been investigated independently in two different fields. Crystalline and amorphous silicon are studied in the field of solid-state physics (i), whereas polysilanes and related molecules are studied in the field of organosilicon chemistry (2). Crystalline silicon (c-Si) and amorphous hydrogenated silicon (a-Si H) are well known as two of the most useful semiconductors for electronic and optical devices. Polysilanes have been investigated for application as SiC ceramic binders (3) and photoresists (4). The methods of synthesizing... 

Interface control at the molecular level is important for the development of molecular electronic junctions [1,2] with potential impact in the fields of molecular memories, photovoltaic conversion and biochemical sensing. In order to achieve homogeneous and reliable long term electrical properties, the design of robust interfaces requires the selection of molecules bearing a chemical functionality reactive towards a solid surface, usually a metal (e.g., gold) or a semiconductor (e.g., hydrogen-passivated crystalline silicon). However, these materials may not be ideal substrates because thiol chemistry produces weak Au-S bonds (167 kJ/mol), while the unreacted Si-H interface bonds at Si(lll) H surfaces are prone to partial oxidation [3],... 

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