Nanostructured semiconductor gas sensors to overcome sensitivity limitations due to percolation effects

Semiconductor gas sensors are widespread in applications to detect toxic or explosive gases. Their gas-sensitive layer consists of a polycrystalline metal oxide film. The gas-detection principle is based on variations of the depletion layer at the grain boundaries in presence of reducing or oxidizing gases which leads to variations in the height of the energy barriers for free charge carriers (e.g. electrons in case of SnO2). The presence of a gas reduces the height of these barriers thus leading to an increased conductivity of the sensing material. The lower detection limit for gases is given by the fact that no (at least single) connected path exists between the reading electrodes below a certain gas concentration. The sensitivity of a gas sensor as well as its dynamic range can be improved significantly when nano technology methods are used to allow for parallel reading of shorter paths.