Characterization of mixed phase silicon by Raman spectroscopy M. Ledinsky ´ * , L. Fekete, J. Stuchlı ´k, T. Mates, A. Fejfar, J. Koc ˇka Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka ´ 10, 162 53 Prague 6, Czech Republic Available online 19 April 2006 Abstract We have examined the common methods for determination of the crystallinity of mixed phase silicon thin films from the TO–LO phonon band in Raman spectra. Spectra are decomposed into contributions of amorphous and crystalline phase and empirical formulas are used to obtain crystallinity either from the integral intensities (peak areas) or from magnitudes (peak maxima). Crystallinity values obtained from Raman spectra excited by Ar + laser green line (514.5 nm) for a special sample with a profile of structure from amorphous to fully microcrystalline were compared with surface crystallinity obtained independently from atomic force microscopy (AFM). Anal- ysis of the Raman collection depth in material composed of grains with absorption depth 1000 nm in an amorphous matrix (absorption depth 100 nm), was used to explain reasons for systematic difference between surface and Raman crystallinities. Recommendations are given for obtaining consistent results. Ó 2006 Elsevier B.V. All rights reserved. PACS: 78.30.Am; 68.37.Ps; 73.63.Bd Keywords: Silicon; Raman scattering; Atomic force and scanning tunneling microscopy 1. Introduction Crystallinity, defined as the volume fraction of crystal- line phase, is the most important characteristic of mixed phase silicon thin films. Most properties of the films (e.g., dark conductivity, absorption coefficient) as well as of the solar cells (V OC ) depend on its value [1]. It is usually deter- mined from the LO–TO peak in Raman scattering spectra, composed of a sharp peak round 520 cm 1 and broad band at 480 cm 1 due to crystalline and amorphous phases. Several techniques have been reported to separate the Raman spectra into amorphous and microcrystalline con- tributions. The easiest and most widely used method is numerical fitting of the spectra by a sum of three Gaussian peaks [2]. The two peaks at around 520 and 500 cm 1 are used to describe asymmetrical crystalline part of the spec- tra. The low energy band (usually situated around 480 cm 1 ) is attributed to the amorphous fraction. Better agreement with the spectra results from using Raman spectrum of pure a-Si:H to represent the amor- phous contribution of mixed phase lc-Si:H Raman spec- trum [3]. This approach was used also in this paper. Once the spectra are decomposed into the amorphous and crystalline components, the crystallinity can be evalu- ated from their integral intensities (areas of bands). How- ever, the value has to be corrected for the Raman scattering cross-sections of the components. Integrated amorphous signal can be expressed as S a = (1  C S )R a V exp where V exp is the scattering volume in the experiment, C S crystalline volume fraction and R a is integrated back scat- tering cross-section of a-Si:H [4]. Integrated crystalline sig- nal is expressed in the same way as S c = C S R c V exp . Solving these two equations for crystalline volume fraction we obtain C S ¼ S c =ðS c þ yS a Þ; ð1Þ where y = R c /R a is the ratio of the integrated cross-sec- tions. The cross-sections were determined from fully amor- phous and fully microcrystalline samples [4] by calculating 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.10.072 * Corresponding author. E-mail address: ledinsky@fzu.cz (M. Ledinsky ´). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 1209–1212