No abstract

The local vibrational modes of hydrogen-induced platelets in crystalline silicon have been studied using infrared absorption and Raman-scattering spectroscopy. Four overlapping but distinct bands are observed in the region 2000-2200 cm . Hydrogen-isotope substitution confirms that these are hydrogenrelated stretching vibrations. Hydrogen concentrations obtained from the integrated infrared band intensities are comparable to total hydrogen concentrations obtained from secondary-ion mass spectroscopy. Relative intensities of the bands depend on sample history and can be varied by annealing. This indicates that the four bands arise from at least three distinct structures. Polarization-sensitive Raman measurements indicate that the Raman-active local modes transform according to the fully symmetric representation of a trigonal point group. One structure possesses distinct ir and Raman-active local modes. We conclude that the platelets are highly ordered structures with fundamental building blocks consisting of silicon atoms with one hydrogen-saturated bond, and that at least one inversion-symmetric structure exists. We compare our results with previously proposed structures.

Results are presented on the effects of growth conditions on hydrogen incorporation in Si thin films deposited with a remote hydrogen plasma. Oxygen contamination of the films was significantly reduced by replacement of the quartz tube that is commonly used to contain the hydrogen plasma with an alumina tube, with a concomitant increase in the electrical conductivity of P-doped a-Si:H films. Hydrogen incorporation was examined with a remote deuterium plasma and downstream injection of SiH4. As the gas flow ratio D2:SiH4 increases, the ratio D:H in the film changes as a consequence of the increasing flux of D at the growing surface. High silane dilution also promotes the formation of microcrystalline silicon, which itself affects H incorporation.

Silicide formation due to thermal treatment of thin (5–10 nm) molybdenum films on single-crystal, polycrystalline, and hydrogenated amorphous silicon substrates in the temperature range of 100 to 1000 °C was studied, with an emphasis on the initial interactions. The molybdenum deposition, annealing, and characterization using Raman scattering and Auger electron spectroscopy was carried out in UHV in order to minimize the effects of contaminants. Raman spectroscopy is used to distinguish between tetragonal (t-MoSi2) and hexagonal MoSi2 (h-MoSi2). The Raman spectrum of bulk tetragonal MoSi2 exhibits two prominent lines which are associated with the A1g (325 cm−1) and Eg (440 cm−1) modes. The only silicide phases detected in the thin film experiments were t-MoSi2 and h-MoSi2. While hexagonal MoSi2 does not appear in the bulk phase diagram, it is the first silicide phase formed in thin film reactions at a temperature between 300 and 400 °C. The nucleation temperature of h-MoSi2 was the same for Si〈100〉, Si〈111〉, and amorphous Si. Indirect evidence for disordered intermixing of silicon and molybdenum before nucleation of h-MoSi2 is found. Annealing at approximately 800 °C causes the silicide to transform from the hexagonal phase to the tetragonal phase for all substrates. Contaminants interfere with the formation of h-MoSi2 and also retard the transformation of h-MoSi2 to t-MoSi2. For the thin films considered here, the transformation to t-MoSi2 is accompanied by islanding of the silicide film. A lower interfacial energy between the silicon and silicide for h-MoSi2 has been proposed to explain the nucleation of h-MoSi2 before t-MoSi2.

No abstract