Tuning field-emission characteristics of ZnO nanorods through defect engineering via O+ ion irradiation

Vertically aligned ZnO nanorods grown by a wet chemical method were implanted with O + ions with three different ion fluences: ( Phi ) = 5 x 10 14, 5 x 10 15, and 5 x 10 16 ions/cm 2. It is observed that the concentration of Oxygen vacancies (O V) introduced by implantation first increases from 25.94 % to 54.76 % with increasing Phi and decreases beyond Phi = 5 x 10 15 ions/cm 2. We attribute this to the knocking out of oxygen atoms from the host matrix, which gets saturated due to the presence of an ample amount of O + ions inside the host matrix beyond Phi = 5 x 10 15 ions/cm 2 and further confirmed by extended x-ray absorption fine structure measurements. Therefore, the abundant O V becomes more delocalized followed by overlapping with the maxima of valence bands resulting in the narrowing of the bandgap of similar to 0.4eV. The appearance of an additional Raman peak at similar to 575 mml:mspace width=.1emmml:mspace cm - 1 in Raman spectra further confirmed the presence of impurity states. It is evident that at a fixed J = 100 mu A/cm 2, the turn-on field increases from 3.61V/ mu m to 6.61V/ mu m with increasing Phi, and as a result of this, the field-enhancement factor ( beta) decreases. We attribute this increase in turn-on field as a consequence of charge trapping in deep-level states created by O V.