Growth and gas sensing characteristics of p- and n-type ZnO nanostructures

ZnO nanoparticles (NPs) of 5–15 nm size and nanowires (NWs) of 50–100 nm dia., exhibiting p and n-type characteristics, respectively, have been synthesized using simple chemical process. ZnO NW-films exhibited good sensitivity and selectivity towards H2S in ppm range with fast response and recovery times. Interestingly, ZnO NP-films showed p-type conductivity that has been obtained for the first time without intentional doping while NW-films showed n-type conduction as has also been reported in various earlier studies. The p- and n-type conductivities in NP- and NW-films have been confirmed using hot probe and Kelvin probe measurements. The n-type behavior of NW-films is attributed to oxygen vacancies, whereas the p-type nature of NP-films is attributed to the zinc vacancy, surface acceptor levels created by the adsorbed oxygen and/or the unintentional carbon doping in ZnO.