Zinc and oxygen vacancies in ZnO nanorods

Abstract

Nominally undoped ZnO nanorods, which have been grown with intentionally incorporated large concentrations of zinc and oxygen vacancies, are studied with electron microscopy and photoluminescence spectroscopy at low temperature. Detailed photoluminescence studies reveal that the concentration of these defects depends on the growth conditions of the nanorods as well as on their annealing history. The optical signatures of these two defects at photoluminescence experiments are related with the 3.31 and 3.235 eV peaks. The activation energies of zinc and oxygen vacancies are calculated to be 123 and 199 meV, respectively.

Study of the photoluminescence emission line at 3.33 eV in ZnO films

“…51 This value is in good agreement with the binding energy of 123 meV above the valence-band maximum calculated for the V 0 Zn in ZnO. 52 Further argument in favor of the attribution of the 3.33 eV emission to the BEs on V 0…”

Zinc related defects in ZnO nanorods

“…1 that the intensity of the peak D, at 3.359 eV, which corresponds to the ABX, follows the change of the intensity of the V Zn peak, while that of the DBX at 3.364 eV follows the Zn i related peak. This behavior, on one hand, confirms our previous [10] assignment of ABX as bound excitons to the zinc vacancy defects, while on the other, shows that the peak DBX is due to the excitons bound to the Zn i related defects which are donors.…”

“…In a previous work [10], we have shown that the 3.308 eV peak is related to a free to acceptor transition with the acceptor being the zinc vacancy, V Zn , with E a ¼ 123 meV, while the optical signature of the corresponding bound exciton, ABX, is the peak at 3.359 eV. Less intense peaks and shoulders, below 3.308 eV, are phonon replicas of the above main peaks, assuming that the LO phonon of ZnO is 72 meV [13].…”

“…From the temperature dependence of DBX we have calculated [10] that the position of the DBX peak at 0 K is at 3.365 eV and its localization energy is 9 meV. One can apply the Haynes rule which, correlates the donor binding energy, E d , with the respective exciton localization energy (E loc ¼ B Â E d þ A), A and B being material constants, in order to check its applicability in this particular case.…”

“…The ZnO nanorods were grown on seeded oxidized silicon substrates by a wet chemical method described in detail elsewhere [9,10]. The seeded substrates were prepared by electron gun evaporation of a 200 nm Ti and subsequent 50 nm ZnO thin film in a high vacuum chamber at room temperature.…”