Electrical conduction mechanism in nanocrystalline ZnO induced by donor/acceptor doping

ZnO nanocrystallites were synthesized using the method of ultrasonication and elements like boron ( B ) and nitrogen ( N ) were doped into ZnO using the same method of preparation. The structural changes studied by X-ray diffraction (XRD) technique include the modification in crystallite size and microstrain in ZnO upon B/N doping. Shifting and broadening of XRD peak positions with doping have also been observed and discussed. Nanosheet like morphology of the doped samples has been observed from the field emission scanning electron microscopic (FESEM) measurement and impurity doping has been confirmed from EDAX and elemental mapping analysis. The increase in boron/nitrogen doping concentration leads to a blue shift of absorption wavelength which results in an increase in the band gap of ZnO. Hall measurement shows a decrease in electrical resistivity of B-ZnO for initial doping concentration of boron but increases for higher concentration. This may be due to the contribution of extra free electrons from B 3+ ions in substituting Zn 2+ in regular sites or in interstitial positions. The increase in resistivity of B-ZnO for higher concentration of boron may be explained on the basis of solubility limit of boron in ZnO lattice. Boron doping also helps in the increase in carrier concentration, conductivity and mobility of carriers in ZnO. For N-ZnO, there is an increase in carrier concentration, mobility and conductivity values with initial doping concentration of nitrogen but decrease thereafter. The carrier type remains as n-type with the resistivity value decreasing with initial doping concentration. P-type conduction is observed in N-ZnO (for higher doping concentration) with increased resistivity which is possible due to the increased (N) O acceptors.