Abstract
Surface photovoltage (SPV) spectroscopy is a powerful tool for studying electronic defects on semiconductor surfaces, at interfaces, and in bulk for a wide range of materials. Undoped and Cobalt-doped TiO2 (CTO) thin films were deposited on Crystalline Silicon (c-Si) and Flourine doped Tin oxide (SnO2:F) substrates by chemical spray pyrolysis at a substrate temperature of 400 °C. The concentration of the Co dopant in the films was determined by Rutherford backscattering spectrometry and ranged between 0 and 4.51 at %. The amplitude of the SPV signals increased proportionately with the amount of Co in the films, which was a result of the enhancement of the slow processes of charge separation and recombination. Photogenerated holes were trapped at the surface, slowing down the time response and relaxation of the samples. The surface states were effectively passivated by a thin In2S3 over-layer sprayed on top of the TiO2 and CTO films.
Highlights
Surface photovoltage (SPV) spectroscopy is a non-destructive and fast technique for investigating optoelectronic properties at surfaces, interfaces, and in bulk by monitoring the illumination-induced changes in the surface voltage [1]
The holes can be trapped at the surface states, resulting in delayed recombination
It can be concluded that the enhancement of the photocatalytic activity of Co-doped TiO2 (CTO) films and nanostructures observed in visible light is mainly due to an increase in the surface defects that are involved in charge separation
Summary
Surface photovoltage (SPV) spectroscopy is a non-destructive and fast technique for investigating optoelectronic properties at surfaces, interfaces, and in bulk by monitoring the illumination-induced changes in the surface voltage [1]. It provides important information, such as surface band bending, surface and bulk carrier separation and recombination, surface state distribution, and defect states by studying the photo-induced carrier separation and transfer in semiconductor materials. Co dopant is optically active, imparts magnetic properties to TiO2 suitable for Spintronics device application, and enhances photocatalytic activity through the introduction of additional electronic defects in its lattice [9,10,11,12]. SPV is a photoelectric method that is very sensitive to changes in electronic states participating in charge separation, independent of whether it is at the surface, interface, or in the bulk [23]
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