Enhancing the photoconductivity and gas sensing performance of TiO₂/SnO₂ heterostructures tuned by the thickness of the SnO₂ upper layer

In this report, polycrystalline TiO₂/SnO₂ heterostructures with variable SnO₂ film thickness were deposited by DC sputtering. Scanning electron microscopy images show a cracked surface in all films. The latter gets more widespread as the SnO₂ layer thickness increases with deposition time. Optical transmittance measurements were used to determine the thickness of the TiO₂ and SnO₂ polycrystalline films. Photocurrent measurements of pure SnO₂ films using UVA irradiation revealed a good response for thinner SnO₂ films, however, these decrease as film thickness increases. Besides, photocurrent response is enhanced for the TiO₂/SnO₂ heterostructures over pure SnO₂ film. It is thought that a high photocurrent response can be produced due to the improved ability to separate the photoinduced electrons and holes, as well as due to suitable charge management at the TiO₂ and SnO₂ interface. Additionally, the large amount of active sites for the thinner SnO₂ upper layer favors better room temperature gas response to ethanol than that obtained for single SnO₂ films. These features make the TiO₂/SnO₂ heterostructure a promising candidate for room temperature gas sensors and photosensitivity applications.