Silicon dangling bonds

III. Hydrogen Interaction with Silicon Dangling Bonds... 

In a porous matrix, the Si-Si bond strength will depend on the atomic configuration. A survey of silicon dangling bond energy in amorphous silicon [6] shows a range from 58 to 130 kJ/mol. 

Figure 5.7. Proposed mechanism for surface hydrosilylation. The initial loss of silicon hydride generates a silicon dangling bond. Reaction between the silicon and an alkene molecule leads to an attached alkyl radical, which may abstract a hydrogen atom from a neighboring silicon.

Of all the gas radicals near the surface, atomic hydrogen can penetrate farthest into the material. The diffusion of hydrogen and its removal and adsorption at the surface, described in Section 2.3.3, show that, at the deposition temperature, interstitial hydrogen can move quite rapidly into the bulk where it readily attaches to silicon dangling bonds. Hydrogen therefore has the fortimate property of being able to remove any subsurface defects left by the deposition process. 

Fig. 4.8. Principal components and angular dependence of the g hift for a silicon dangling bond.

Table 4.1. Wavefunction coefficients in Eq. (4.14) for silicon dangling bonds in different environments...

Furthermore, the broad TMS signal is similar to the reported silicon-dangling bond centers observed from silane plasma deposition [13,14]. In addition, a well-studied class of paramagnetic silicon defects, the Pb centers [15,16], has precisely the g anisotropy (fig 0.006) required to account for the width of the TMS signal. The overall effect of including all these Pb defects together would be to... 

As mentioned in the previous section, the commonly accepted microscopic interpretation of the ESR response in a-Si and a-Si H is in terms of a highly localized silicon dangling bond. It is important at this point to examine the evidence for this interpretation. We mentioned in Section 5 the comparison between an ESR response observed on single crystal Si surfaces and the ESR in a-Si. A second comparison of interest is the ESR from Si-Si02 interfaces (Caplan et ai, 1979), where an axially symmetric response is observed (g, — 2.001, = 2.008), which is most probably due to a... 

In doped samples three different ESR responses are observed the usual silicon dangling-bond resonance, a broad resonance attributed to holes trapped in states near the valence-band edge, and a narrow resonance attributed to electrons trapped in states near the conduction-band edge. Two interpretations have been proposed for the presence of these two additional signals—holes or electrons trapped at weak bonds in the band tails and holes or electrons trapped at twofold-coordinated silicon defect sites. 

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