Determination of Raman emission cross-section ratio in hydrogenated microcrystalline silicon E. Vallat-Sauvain * , C. Droz, F. Meillaud, J. Bailat, A. Shah, C. Ballif Institute of Microtechnology, University of Neucha ˆtel, rue Breguet 2, CH-2000 Neucha ˆtel, Switzerland Available online 17 April 2006 Abstract The determination of the crystalline volume fraction from the Raman spectra of microcrystalline silicon involves the knowledge of a material parameter called the Raman emission cross-section ratio y. This value is still debated in the literature. In the present work, the determination of y has been carried out on the basis of quantitative analysis of medium-resolution transmission electron microscopy (TEM) micrographs performed on one layer deposited by very high frequency plasma enhanced chemical vapor deposition (VHF- PECVD) close to the amorphous/microcrystalline transition. Subsequent comparison of these data with the crystallinity as evaluated from measured Raman spectra yields a surprisingly high value of y = 1.7. This result is discussed in relation to previously published val- ues (that range from 0.1 to 0.9). Ó 2006 Elsevier B.V. All rights reserved. PACS: 78.30.Ly; 78.67.Bf Keywords: Raman scattering; STEM/TEM; TEM/STEM; Microcrystallinity 1. Introduction The degree of crystallinity of hydrogenated microcrys- talline silicon (lc-Si:H) is an important measure for both layer and device characterization. Indeed, several material quality parameters such as defect density, dark- and photo- conductivity and device properties such as open-circuit voltage (V oc ) depend mainly on the degree of crystallinity of the microcrystalline silicon intrinsic layer. The com- monly used experimental technique for the quantification of crystallinity in microcrystalline silicon is Raman spec- troscopy. Indeed, it is a desktop, fast and non-destructive measurement technique. In a Raman spectrum, the amor- phous silicon phase of the lc-Si:H leads to the appearance of a broad peak centered at 480 cm 1 , whereas the nano- crystalline silicon phase leads to the occurrence of an asym- metric peak centered at 520 cm 1 . The low-wavenumber tail of this peak (around 510 cm 1 ) is attributed to the defective but yet crystalline part of the nanocrystals. Inte- grated intensities of both phases (I a and I c , respectively) can be easily evaluated from the Raman spectra, and their ratio yields the so-called ‘Raman crystallinity factor’ / c [1]. This value is not identical with the actual crystalline vol- ume fraction X c which involves the additional parameter y in the following way [2,3]: X c = I c /(I c + yI a ) where y is the ‘Raman emission cross-section ratio’. The value of y is at present a matter of debate. Values from 0.88 down to 0.1 have been published [2,3]. Further- more, y basically depends on the size of the crystallites and on the excitation wavelength used for the Raman experi- ment [2]. Thus, Raman emission cross-section ratio values for the amorphous and nanocrystalline phases are not at all known, with the necessary precision, for a quantitative evaluation of the crystallinity in lc-Si:H. Here, we report on quantitative analysis of the amor- phous/microcrystalline phases present in lc-Si:H from transmission electron microscopy (TEM) micrographs and their relationship with the measured Raman crystallin- ity factors. From this comparison, a value is obtained for y. 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.11.128 * Corresponding author. Tel.: +41 32 718 32 00; fax: +41 32 718 32 01. E-mail address: Evelyne.Vallat@unine.ch (E. Vallat-Sauvain). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 1200–1203