Abstract
Nanocrystalline ZnO, ZnO(Ga), and ZnO(Ga, In) samples with different indium contents were prepared by wet-chemical method and characterized in detail by ICP-MS and XRD methods. Gas sensing properties toward NO2 were studied at 150–450 °C by DC conductance measurements. The optimal temperature for gas sensing experiments was determined. The dependence of the ZnO(Ga, In) sensor signal to NO2 at 250 °C correlates with the change of conductivity of the samples. The introduction of indium into the system leads to an increase in the values of the sensor signal in the temperature range T < 250 °C. The investigation of the local sample conductivity by scanning spreading resistance microscopy demonstrates that, at high indium content, the sensor properties are determined by the In–Ga–Zn–O layer that forms on the ZnO surface.
Highlights
IntroductionZinc oxide is a wide-gap semiconductor (band gap 3.4 eV), which is used as a material for transparent electrodes, optoelectronic converters, luminescent devices, catalysts, and gas sensors [1]
Zinc oxide is a wide-gap semiconductor, which is used as a material for transparent electrodes, optoelectronic converters, luminescent devices, catalysts, and gas sensors [1].Non-doped zinc oxide is an n-type semiconductor
In this work we investigated nanocrystalline ZnO(Ga, In) materials as gas sensors for the detection of NO2 at sub-ppm concentration
Summary
Zinc oxide is a wide-gap semiconductor (band gap 3.4 eV), which is used as a material for transparent electrodes, optoelectronic converters, luminescent devices, catalysts, and gas sensors [1]. Non-doped zinc oxide is an n-type semiconductor. The main types of point defects are interstitial zinc atoms and oxygen vacancies, which are responsible for the deviation of the composition of Zn1+δ O from stoichiometry [1,2]. The most interesting is nanocrystalline zinc oxide with a particle size of less than 50 nm [3]. Nanocrystalline zinc oxide usually is highly resistive, since the large surface facilitates the chemisorption of acceptor molecules of oxygen. Doping of zinc oxide with M3+ cations, which can be incorporated into ZnO crystal lattice and act as donor impurities, allows increasing the conductivity of the material [4]. Trivalent cations Ga3+ and In3+ have the closest values of the effective ionic radii to that of Zn2+ [5]
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