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

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.