On the photo-induced electrical conduction related to gas sensing of the Sb:SnO2/TiO2 heterostructure

Abstract

In this work, changes on the electrical properties as function of the temperature and gas addition on the surface of the 4at%Sb:SnO 2 /TiO 2 heterostructure are investigated. This heterojunction privileges the gas sensor application at temperatures nearer to the ambient temperature, when compared to existing devices, which is more efficient when sensitized with monochromatic light of specific wavelength. The results point that the conduction mechanism, under the thermally activated trapping influence, is occurring preferentially in the TiO 2 layer, since the activation energy of the deepest level is 56 meV, comparable to donors from TiO 2. Besides, an increase of the photo-current decaying rate was noticed when using the excitation of a He-Cd laser under O 2 atmosphere and room temperature, compared to films with a sole TiO 2 layer. Samples showed a high resistance variation (up to 40 times) with the addition of gas at temperatures higher than 330 K, that can be attributed to the electron trapping by the oxygen molecules adsorbed on the sample surface. A model that describes such trap-states and the conduction mechanism within the samples is proposed. This way, this work can be valuable to the better understanding of the effects and rules on the electrical behavior of this heterostructure, in order to apply this material as a gas sensor device.

Crystallization and electrical measurements of sintered qandilite (Mg2TiO4)-borosilicate glass composite

“…This finding is consistent with the sample's conductivity increasing to 9.32 × 10 -7 S m −1 . Such a decrease of activation energy can be related to the possibility of the formation of Ti 4+ and Ti 3+ ions which may cause the electronic mechanism to take precedence over the ionic transfer mechanism, and also may come from interstitial Ti 3+ and oxygen vacancies causing the n-type conductive nature of TiO 2 [45,46].…”

Blue sensitive sub-band gap negative photoconductance in SnO2/TiO2 NP bilayer oxide transistor

“…35 This charge transfer leads to a potential barrier at the SnO 2 /TiO 2 interface. 36 However, in this bilayer heterostructure, electrons are allowed to independently transfer through the SnO 2 or TiO 2 layer under external bias. In the case of SnO 2 /TiO 2 bilayer lateral devices like TFT, electron will most likely transfer through the SnO 2 layer owing to its considerably high carrier mobility than that of TiO 2 .…”

Narrowband Red-Sensitive Positive−Negative Reversible Photodetector Using Organic Dye on the TiO2/SnO2 Heterojunction

“…Among different classes of materials, metal oxide heterostructure-based NPC photodetectors are environmentally stable and show a systematic variation due to their wide-band-gap nature and high electron mobility . During heterojunction formation, based on the electron affinity difference between the two semiconductors, electrons can migrate from one to the other, until equilibrium is attained. , Among different heterostructures, SnO 2 /TiO 2 has been used for UV detection, UV-activated formaldehyde sensing gas sensing, and sensory gas chromatography. − In the case of a SnO 2 /TiO 2 ( n−n- type semiconductor) heterostructure, the equilibrium condition leads to electron transfer from SnO 2 to TiO 2 , due to the higher electron affinity of TiO 2 (4.6 eV) when compared to SnO 2 (4.2 eV) . This creates a potential barrier at the interface, which restricts the transfer of photogenerated electrons from TiO 2 to SnO 2 , and hence carrier density is increased at the TiO 2 surface.…”