Experimental and numerical study of cw green laser crystallization of a-Si:H thin films O. García , D. Munoz-Martin , J.J. García-Ballesteros , Y. Chen , M. Morales , J. Cárabe , J.J. Gandía , C. Molpeceres 1.     cnica de Madrid, Campus Sur UPM, Ed. La Arboleda, Ctra. de Valencia, km, 7,300, 28031 Madrid, Spain 2. CIEMAT, Av. Complutense 40, 28040 Madrid, Spain Crystallization and grain growth technique of thin film silicon are among the most promising methods for improving efficiency and lowering cost of solar cells. A major advantage of laser crystallization and annealing over conventional heating methods is its ability to limit rapid heating and cooling to thin surface layers[1-3]. Laser energy is used to heat the amorphous silicon thin film, melting it and changing the microstructure to polycrystalline silicon (poly-Si) as it cools. Depending on the laser density, the vaporization temperature can be reached at the center of the irradiated area. In these cases ablation effects are expected and the annealing process becomes ineffective. The heating process in the a-Si thin film is governed by the general heat transfer equation [4-5]. The two dimensional non-linear heat transfer equation with a moving heat source is solve numerically using the finite element method (FEM), particularly COMSOL Multiphysics [6]. The numerical model help to establish the density and the process speed range needed to assure the melting and crystallization without damage or ablation of the silicon surface. The samples of a-Si obtained by physical vapour deposition were irradiated with a cw-green laser source (Millennia Prime from Newport-Spectra) that delivers up to 15 W of average power. The morphology of the irradiated area was characterized by confocal laser scanning microscopy (Leica DCM3D) and Scanning Electron Microscopy (SEM Hitachi 3000N). The structural properties were studied by micro-Raman spectroscopy (Renishaw, inVia Raman microscope) [7]. Fig. 1 a) Experimental crystalline fraction (Φ c ) profile measured on the surface of the sample along a perpendicular line to the laser processed track. b) Numerical temperature profile at a cross section of the sample perpendicular to the laser processed track. The process parameters predicted by the numerical model are consistent with those experimentally observed. Acknowledgements This work has been supported by the Spanish Ministry of Science and Innovation under projects AMIC ENE2010-21384- C04-02, SIMLASPV ENE2011-23359 and INNDISOL IPT-420000-2010-6 (FEDER funded “Una manera de hacer Europa”). References 1 Nickel, N. H. Laser Crystallization of Silicon - Fundamentals to Devices, Semiconductors & Semimetals, Volume 75. (Elsevier Academic Press, Amsterdam, 2003). [2] S.J. Park, Y.M. Ku, E.H. Kim, J. Jang, K.H. Kim, C.O. Kim, Selective crystallization of amorphous silicon thin film by a CW green laser, Journal of Non-Crystalline Solids. 352 (2006) 993–997. [3] G. Andra, J. Bergmann, F. Falk, Laser crystallized multicrystalline silicon thin films on glass, Thin Solid Films. 487 (2005) 77–80. [4] Z. Yuan, Q. Lou, J. Zhou, J. Dong, Y. Wei, Z. Wang, et al., Numerical and experimental analysis on green laser crystallization of amorphous silicon thin films, Optics & Laser Technology. 41 (2009) 380–383. [5] O. García, J.J. García-Ballesteros, D. Muñoz-Martín, S. Núñez-Sánchez, M. Morales, J. Cárabe, et al., Estimation of Local Crystallization of a-Si:H Thin Films by Nanosecond Pulsed Laser Irradiation Through Local Temperature Simulation, Physics Procedia. 39 (2012) 286–294. [6] COMSOL Multiphysics Reference Manual, version 4.1, COMSOL, AB., 2010. [7] C. Smit, R. van Swaaij, et al., Determining the material structure of microcrystalline silicon from Raman spectra, Journal of Applied Physics 94 (5), 3582-3588, 2003. View publication stats View publication stats