Growth And Characterization Of Large Grained Poly-Si Films Grown On Biaxially Textured Ni-W Substrate By Hot-wire CVD

Physics of Energy Harvesting Division, Council of Scientific & Industrial Research (CSIR) - National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012, India

Adv. Mater. Lett., 2015, 6 (5), pp 436-441

DOI: 10.5185/amlett.2015.5754

Publication Date (Web): May 05, 2015

Copyright © IAAM-VBRI Press

E-mail: kmk_srivatsa@mail.nplindia.org

Abstract

Polycrystalline Si (Poly-Si) film with highly crystalline nature, and having most of the grains in the range of 50-100 µm has been grown over biaxially textured Ni-W substrate by Hot-wire chemical vapor deposition technique, using a single buffer layer of CeO₂ thin film. This result has been achieved for the SiH₄ source gas diluted to 95% with added H₂ gas, and for the substrate temperature of 840±10oC and a deposition pressure of 40 mTorr. XRD analysis shows that the Poly-Si films have grown with (111) and (200) orientations. Raman studies reveal that a crystalline volume fraction of 95.3% has been achieved. The imaginary part of pseudo dielectric function, <ε₂>, as extracted from ellipsometric data, shows two prominent shoulders at energy positions 3.4 eV and 4.2 eV corresponding to the optical absorption of crystalline Si, indicating a high crystallinity of the Poly-Si film. SEM micrograph shows that the grown Poly-Si film is following the morphology and grain size as that of biaxially textured Ni-W substrate. SIMS analysis of the total multilayer structure shows a formation of very sharp interfaces, with no diffusion between Si and Ni, indicating that a single buffer layer of CeO₂ is sufficient to avoid the formation of nickel silicide while growing Si over Ni substrate. Thus, these results are very encouraging for the fabrication of Poly-Si film based solar cells with increased efficiency by minimizing the undesired recombination of charge carriers at grain boundaries.

Keywords

Poly-Si film, CeO₂ buffer layer, hot-wire CVD, Raman spectra, ellipsometer.