Structural and electrical anisotropy and high absorption in poly-Si films prepared by catalytic chemical vapor deposition

Structural, electrical and optical properties of polycrystalline Si (poly-Si) films prepared by catalytic chemical vapor deposition (cat-CVD) method, often called hot-wire CVD method, are demonstrated. Crystalline fraction for the poly-Si films is easily controlled between about 0% and 80% by changing the flow-rate ratio of SiH4 to H-2 during deposition. Transmission electron microscopy (TEM) observation reveals that cat-CVD poly-Si films with large crystalline fractions consist of columnar grains surrounded with an interlayer amorphous phase. Directional anisotropy in electrical conductivity is also observed, which is correlated with the structural anisotropy observed by TEM. Differences in the property of an amorphous layer in the poly-Si films is also indicated by the temperature-dependence of the conductivity. The origin of the absorption coefficient of cat-CVD poly-Si films is also discussed. (C) 1998 Elsevier Science B.V. All rights reserved.