Quantification of the bond-angle dispersion by Raman spectroscopy and the strain energy of amorphous silicon

Abstract

A thorough critical analysis of the theoretical relationships between the bond-angle dispersion in a-Si,⌬ , and the width of the transverse optical Raman peak, ⌫, is presented. It is shown that the discrepancies between them are drastically reduced when unified definitions for ⌬ and ⌫ are used. This reduced dispersion in the predicted values of ⌬ together with the broad agreement with the scarce direct determinations of ⌬ is then used to analyze the strain energy in partially relaxed pure a-Si. It is concluded that defect annihilation does not contribute appreciably to the reduction of the a-Si energy during structural relaxation. In contrast, it can account for half of the crystallization energy, which can be as low as 7 kJ/mol in defect-free a-Si.

Can the crystallization rate be independent from the crystallization enthalpy? The case of amorphous silicon

“…In this case, the epitaxial crystallization rate of a 2 µm thick amorphous region obtained by ion implantation on a c-Si wafer remained essentially the same (within an error bar of 3%) before and after partial structural relaxation. From the Raman spectra of that sample, we can estimate [36] that the crystallization enthalpy diminished from 812 to 605 J g −1 (i.e., by 60 meV/atom) due to structural relaxation.…”

Light induced electrical and macroscopic changes in hydrogenated polymorphous silicon solar cells

“…To minimize the influence of the weak vibrational modes, LA and LO, one can perform a best fit on each spectrum from 250 to 550 cm −1 by three Gaussian curves and a straight base line [24]. The RMS bond angle deviation was deduced using the following formula, proposed by Beeman et al [27,28]. Figure 3 shows the TO peak position and δθ change during light-soaking.…”

Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

“…Recently, we have shown that before crystallization begins, structural relaxation processes stop near 8.7°because most of the mobile defects, whose diffusion facilitates network restructuring, have already recombined. 3,5 This conclusion leaves the door open to the possibility of reaching a higher degree of relaxation if alternative mechanisms for network restructuring were to come into play. In that case, further diminution of ⌬ would be possible and, eventually, a value of ⌬ below 6.6°could be reached if the real minimum value of ⌬ were lower than predicted.…”