2.10 Doping of nanostructures

Doping of the nanowires and nanorods through in situ or post processing techniques will provide a far more favorable approach to modulate their electrical, optical, and piezoelectric properties. Most metal dopant ions result in the increase of density of the conduction carriers by occupying the lattice sites in the ZnO crystal. The complete picture of the crystal can be changed by changing the doping level. The controlled modification of morphological features as well as enhancement of electrical and optical properties can be achieved by introducing dopant element in metal oxide semiconductor [45]. The electrical as well as optical properties of MOS can be tuned by adding the foreign elements or by the alternation of oxygen stoichiometry. By making these changes, one can get an increase in carrier's concentration, electrical resistivity, and mobility [45]. Doped nanostructure-based sensors are fully capable of sensing different harmful gases, with good stability, selectivity, and sensitivity. Out of many other methods, doping is considered to be one of the best methods for enhancement of gas sensing properties of ZnO nanostructures at room temperature. Doped ZnO nanostructures were used in the past by many researchers for the detection of harmful gases in the environment. For example, the gas sensing properties of Sn-doped ZnO nanostructures were investigated by S.C. Navel and I.S. Mulla using the thermal evaporation method. The results show good response to different gases for pure Sn-doped nanostructures, in temperature range of 275°C to 300°C. They proved that the sensitivity toward UV sensing can be increased by the doping of Sn material [46].
