Preparation of ZnO nanorod arrays with tailored defect-related characterisitcs and their effect on the ethanol gas sensing performance

In this study gas sensors using ZnO nanorod arrays (NRs) with different surface-to-volume ratios and tailored defect-related properties are prepared and used to fabricate gas sensors. There are three kinds of ZnO gas sensors (ZnO seed layer and different ZnO NRs) grown by sol–gel route and subsequent aqueous chemical growth (ACG). The variation in sensing performance to ethanol gas of those gas sensors will be discussed in terms of morphology and the defect-related carrier behavior of ZnO NRs. Furthermore, the I–V characteristics (metal–semiconductor contact) of ZnO NRs are used to elucidate the defect-related properties affecting the electrical properties of ZnO as well as the sensitivities of those ZnO NRs. The ZnO NRs grown with Zn salt/KOH solution have a larger intensity of deep level emission and a higher Fermi level than that grown with Zn salt/HMTA solution, and sensitivity to ethanol gas of the former is superior. Therefore, it is proposed that more oxygen vacancy inducing more free carriers for gas sensing will result in a higher sensitivity to ethanol gas for sensors based on ZnO nanorod arrays.