Metal oxide p-n homojunction

Normally, metal oxides such as SnO, TiO, WO3, ZnO, and Inj03 usually used for gas sensor design are n-type semiconductors (see Fig. 2.27). However, there are few metal oxides such as CrO, CuO, and NiO that also exhibit p-type conductivity (Krilov and Kisilev 1981 Stamataki et al. 2008). Recently p-type conductivity was reported in ZnO (Basu and Hazra 2005 Hazra and Basu 2006). Thus, the fabrication of semiconducting metal oxide p-n homojunctions could also be achieved with ZnO. It was shown that p-n ZnO homojunction is sensitive to H as there is a substantial shift in the forward bias I-V characteristics on exposnre to the reducing gases (Basu and Hazra 2005 Hazra and Basu 2006). 

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