Heterogeneity in hydrogenated silicon: Evidence for intermediately orderedchainlike objects - art. no. 125338

Hydrogen (H-2) dilution of the source gas is known to be a key factor in pr oducing hydrogenated amorphous silicon films that demonstrate a high degree of optoelectronic stability. In this work, we investigate, using Raman spe ctroscopy and high-resolution transmission electron microscopy (TEM), wheth er microstructural differences exist between such films and those made with no H-2 dilution (i.e., that have greater instabilities). The key variable is the H-2 dilution, which ranges from none to very high levels, producing amorphous and microcrystalline silicon films. The TEM results show that emb edded within the amorphous matrix are chainlike objects (CLO's) having simi lar to3 nm widths, similar to 30 nm lengths, and showing a high degree of o rder along their length. Such order implies vanishing levels of bond-angle distortion (BAD). These CLO's are present in all samples investigated, but their density increases with the level of H-2 dilution. The Raman spectra s how a TO band centered at 490 cm(-1) (37+/-3 cm(-1) full width). Quantitati ve analysis shows this band to exist in all samples investigated, but incre ases in magnitude with increasing H-2 dilution. In the highest dilutions wh en microcrystallites are observed, the band is distinctly evident. Its posi tion and width are also consistent with very low (crystallinelike) levels o f BAD similar to0 degrees. It is thus likely the 490 cm(-1) Raman band is a signature of the intermediate ordered CLO's.