Effects Of Doping On The Gas Sensing Properties Of ZnO Nanowires

Single element(Ga,In,Sn) doped ZnO nanowires and dual elements(In-Sn)co-doped ZnO nanomaterials and three elements(Ga-In-Sn)doped ZnO nanomaterials were synthesized by thermal evaporation method. The morphology, microscopic defects and the chemistry state of doping elements of ZnO nanomaterials were characterized by electron microscope(SEM), high resolution transmission electron microscope(HRTEM),Photoluminescence(PL) and X-ray photoelectron spectroscopy(XPS),and the ethanol,CO,NO2,SO2gas sensing properties have been tested by CGS-1TP intelligent gas sensing analysis system. Band structure and the electronic structure of ZnO nanomaterials were studied by first-principles calculation. Besides, we further discussed a correlation between the gas sensing properties and the doping elements. The gas sensing mechanism model was made, and the CO gas sensing theoretical mechanism of single element doped ZnO have been analysised. The results are as following:1) Morphology of different concentrations of Ga-doped ZnO have significantly changes. Ga3+is the chemical state of Ga element in ZnO, and Ga doping leads to smaller band gap and changes density of states of ZnO. Two kinds of surface defects are found in the crystal structure of In-doped ZnO, In3+exists in ZnO crystal. The number and density of crystals increase significantly in the conduction band bottom and in the local parts of top valence band of In-doped ZnO crystal. In the In Sn co-doped ZnO crystal, Zn2+is displaced by Sn4+, and ZnO band gap is effected by the doping of Sn.2) The4%mol Ga-doped ZnO nanomaterials have high sensitive responds to CO, which is4.59, but the working temperature(270℃) is too high. Compared with single element of doping ZnO, Ga-In-Sn doped ZnO has a higher sensitivity (6.02) to CO. However, for NO2gas, the three elements doped ZnO nanowires have bad gas sensing performance and even not patch on the sensitive responds of Sn-doped ZnO, in which the5mol%Sn-doped ZnO have the maximum sensitivity(204.8) to NO2. As well,Sn doped ZnO have the best performance to SO2. Sn-doped ZnO nanowires have the highest sensitive responds to ethanol,while In-doped ZnO shows the shortest response and recovery times.3) First-principles calculation results show that the Ga-doped modified ZnO sensing mechanism of CO is mainly the Ga-doped ZnO (001) surface adsorption energy relative increases, bond length changes. Ga-doped ZnO surface occurrence a significant change in the electronic density of states before and after the adsorption of of the CO, and the Fermi level into the conduction band. CO has a strong Electron-donating ability, surface states in the conduction band bottom energy level enhanced since the electronic transactions from CO, and Ga-doped semiconductor produce more electrons in the surface lead to resistivity decrease and more gas molecules adsorbed, showing superior CO gas sensitive properties.