H. Touir et al., Local Si-H bonding environment in hydrogenated amorphous silicon films in relation to structural inhomogeneities, PHYS REV B, 59(15), 1999, pp. 10076-10083
The hypothesis of the relation between the local environment of polyhydride
[(SiH2)(n)] groups and structural inhomogeneities (due to the presence of
voids) of an amorphous silicon network has been tested in hydrogenated amor
phous silicon films prepared by rf magnetron sputtering (RF MS). Comparativ
e infrared (IR) absorption, Raman spectroscopy and optical transmission mea
surements have been performed on samples deposited under the same plasma co
nditions at various substrate temperature (T). The results of the IX studie
s show that all samples exhibit the same hydrogen content incorporated as i
solated monohydride (SiH) groups responsible for the absorption band at 200
4 cm(-1). As a consequence, the gradual decrease in the total bonded hydrog
en content as T increases is essentially due to the decrease in the amount
of hydrogen bonded as polyhydride [(SiH2)(n)] groups which absorb around 20
86 cm(-1). A direct relationship is established between the changes in the
IR spectra and the variation of structural inhomogeneities observed by Rama
n spectroscopy. The linewidth in the low-frequency side of the transversal
acoustic (TA) -like band in the Raman spectra decreases monotonously as T i
ncreases. This decrease is attributed to a decrease in density of quasiloca
lized vibrational modes in structural inhomogeneities (disordered domains a
round the surface of voids) in the amorphous network. The good correlation
between the IR and Raman results indicates that the (SiH2)(n) groups are lo
cated in structural inhomogeneities due to the presence of voids in the amo
rphous network where the formation of these complexes is favorable. This in
terpretation is corroborated by the variation of both the static refractive
index, which gives information about the density of material, and the disp
ersion energy, which measures the mean coordination number of Si atoms and
the effective number of valence electron per Si atom in the amorphous netwo
rk. [S0163-1829(99)02608-9].