Drastic Resistivity Reduction of CVD-TiO₂ Layers by Post-Wet-Treatment in HCl Solution

Abstract

Poly-crystalline anatase TiO₂ layer fabricated by LPCVD using titanium-tetra-iso-propoxide and NbF₅ in H₂-ambient was treated in conc.-HCl solution after thin layer of IIIb-group metal was deposited on the TiO₂ layer. Resistivity of the as-deposited layer about 1 × 10^-1 Ω · cm was drastically reduced to 3 × 10^-3 Ω · cm by the wet-treatment using indium. Temperature dependence of the resistivity increased with temperature above 100 K for the wet-treated layer was quite different from that decreased above 100 K for the as-deposited layer, whereas the resistivity was saturated at lower temperatures. The resistivity at room-temperature was decreased with the thickness before the wet-treatment but independent on the thickness above 100 nm for the wet-treated layer. Indium was more effective for the resistivity reduction than gallium but aluminum was not useful for the treatment. As the results that the wet-treatment using indium was examined for the TiO₂ layers deposited by various conditions, the optimum deposition condition to reduce the resistivity of the layer after the wet-treatment was clearly different from that for the as-deposited layer.