Eur. Phys. J. Appl. Phys.
Volume 39, Number 3, September 2007
|Page(s)||203 - 209|
|Section||Semiconductors and Related Materials|
|Published online||12 July 2007|
Raman spectroscopy of nano-structured silicon to study the embedded crystallites
Samtel Center for Display Technologies, Indian Institute of Technology 208016 Kanpur, India
2 Dept. of Physics, Indian Institute of Technology, Kanpur-208016, UP, India
3 LPICM, Ecole Polytechnique, 91128 Palaiseau Cedex, France
Corresponding author: email@example.com
Accepted: 5 June 2007
Published online: 12 July 2007
Raman spectra of a variety of polymorphous (pm-Si:H) and amorphous silicon (a-Si:H) samples deposited by plasma enhanced chemical vapor deposition (PECVD) at different pressures were recorded in the range of 150 cm-1 to 750 cm-1 using a 514 nm excitation source. A comparison of Raman spectra between a-Si:H and pm-Si:H samples reveals significant differences. The Transverse Optical (TO) peak in case of pm-Si:H is asymmetric and shifted to higher wave numbers. In the literature, discrepancies between predictions of various quantum confinement models and experimental spectra have typically been attributed to either strain or negligible fraction of nanocrystallites. We show that a quantum confinement model along with a Gaussian size distribution is able to accurately predict particle size of nanocrystallites embedded in the amorphous matrix. The crystallite size and size distribution obtained by fitting the TO peak is consistent with high-resolution transmission electron microscopy observations. In our case typical mean crystallite size obtained is about 3 nm with FWHM of the distribution varying in the range 0.2–1 nm. A comparison of ratio of heights in TA and TO peaks of a-Si:H and pm-Si:H material indicates that pm-Si:H as a material has higher medium range order (MRO). This ratio has been used to compare the degree of MRO in pm-Si:H samples prepared under different conditions. Thus, we demonstrate that Raman Spectroscopy along with our model can be used to obtain the crystallite size distribution and provide a measure of degree of medium range order.
PACS: 78.67.Bf – Nanocrystals and nanoparticles / 78.66.Jg – Amorphous semiconductors; glasses / 78.30.Ly – Disordered solids
© EDP Sciences, 2007
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