Morphological, structural, and electrical properties of PbS thin films deposited on HfO2, SiO2, and Al2O3 for TFTs applications

PbS thin films were deposited by the chemical bath deposition (CBD) technique at 43 °C on HfO2, SiO2, and Al2O3 dielectric films, which were previously deposited by atomic layer deposition (ALD) on <100> silicon wafers. The effect of the dielectric surface on the final morphology and structure of the PbS films was studied to find the most suitable dielectric/PbS system for thin film transistors (TFTs) applications. The PbS films showed a polycrystalline structure related to the galena cubic phase. The surface morphology of the PbS films was analyzed by scanning electron microscopy (SEM), which evidenced a gradual coverage of the surface of the dielectric with the deposition time. The shape of the PbS grains evidenced a strong dependence with the dielectric substrate employed. The PbS films deposited on HfO2 achieved a well-defined and compact microstructure in comparison with the other dielectric substrates. The electrical properties of the PbS films were studied by Hall effect measurements. A p-type conductivity with Hall mobility up to 0.44 cm2V−1cm−1 and electrical resistivity values between 102-105 Ωcm were obtained. Finally, two TFTs were fabricated by using standard photolithography processes, where the PbS film was used as semiconductor active layer and HfO2 (30 nm) as dielectric gate layer, respectively. The electrical response of the PbS-based TFTs evidenced a p-type behavior with a mobility in the saturation regime (μsat) in the range of 0.006–0.011 cm2/Vcm and ION/IOFF current ratio in the order of 102. The TFTs operated in depletion mode with a low positive threshold voltage (VTH) between 0.5 and 2 V.