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Abstract: H2 additional effect for crystallization of SnO2 films prepared by the hot-wire CVD method was investigated. The crystallization of SnO2 films starts at 170°C. The selectivity enhancement of the solar cell substrate will contribute to reduce the cost of silicon thin film solar cells. The atomic hydrogen assisted nano-crystallization exists for the depositions of SnO2 films by the hot-wire CVD method. Furthermore, the addition of H2 gas improved the electrical conductivity up to 5.3×100 S/cm. However, these effects are limited in the deposition condition of a small amount of hydrogen. Addition of much higher hydrogen concentration starts an etching effect of oxygen atoms. [Copyright &y& Elsevier]

Abstract: Nb-doped TiO2 films have been fabricated by RF magnetron sputtering as protective material for transparent-conducting oxide (TCO) films used in Si thin film solar cells. It is found that TiO2 has higher resistance against hydrogen radical exposure, utilizing the hot-wire CVD (catalytic CVD) apparatus, compared with SnO2 and ZnO. Further, the minimum thickness of TiO2 film as protective material for TCO was experimentally investigated. Electrical conductivity of TiO2 in the as-deposited film is found to be ∼10−6 S/cm due to the Nb doping. Higher conductivity of ∼10−2 S/cm is achieved in thermally annealed films. Nitrogen treatments of Nb-doped TiO2 film have been also performed for improvements of optical and electric properties of the film. The electrical conductivity becomes 4.5×10−2 S/cm by N2 annealing of TiO2 films at 500°C for 30min. It is found that the refractive index n of Nb-doped TiO2 films can be controlled by nitrogen doping (from n=2.2 to 2.5 at λ = 550nm) using N2 as a reactive gas. The controllability of n implies a better optical matching at the TCO/p-layer interface in Si thin film solar cells. [Copyright &y& Elsevier]

Impurity doping using B2H6 gas using hot-wire CVD has been tried for hydrogenated amorphous silicon-carbon (a-SiCX:H) alloy films including hydrogenated microcrystalline silicon (μc-Si:H) with carbon content, C/(Si+C), of about 28%. The dark- and photoconductivities of B-doped samples are larger than those of undoped samples. The activation energy for dark conductivity of the B-doped sample with the doping gas ratio, B2H6/(SiH4+CH4), of about 0.054% is 0.17 eV. This value is smaller than that of the undoped sample. The P-doped samples also show larger dark- and photoconductivities and smaller activation energy than the undoped samples. [Copyright &y& Elsevier]