Optoelectronic Characterization of ZnO Nanorod Arrays Obtained by Pulse Electrodeposition

Abstract

ZnO nanorod arrays have been grown by potentiostatic pulse electrodeposition between a reduction potential and a "rest" potential. The effect of the duty cycle and pulse frequency as well as the heat-treatment in air on the properties of the electrodeposits has been studied. Surface morphology, structural, optical and electrical properties were evaluated. Absorption spectra reveal a high energy bandgap Burstein-Moss shift for the as-grown nanorods, in line with the donor density (1.1 × 10 19 and 9.5 × 10 19 cm −3 ) determined from electrochemical impedance spectroscopy. After annealing, the carrier concentration decreases to 10 17 -10 18 cm −3 , which is accompanied by an increase of the optical quality of the samples, assessed by the narrowing of the full width at half maximum of the near band edge recombination and steeper absorption at ∼3.3 eV. The donor density and the flatband potential are dependent of the applied duty cycle and pulse frequency. All the analyzed samples evidence deep broad emission bands in the visible region, whose intensity is enhanced after annealing. The defect luminescence is due to an overlap of emitting centers in the red, yellow and green spectral regions, as evidenced and discussed by comparing the steady-state and transient spectroscopies.

Electrochemical and photoluminescence response of laser-induced graphene/electrodeposited ZnO composites

“…The presence of broad bands in the visible spectral region is very frequent in ZnO crystals, both in bulk and in micro/nanostructures 57 . Indeed, the existence of orange/red luminescence bands has been widely reported in the literature 58 , 59 , especially in the case of low temperature synthesized materials 18 , and particularly in the ones prepared by electrodeposition 21 , 60 , 61 . The assignment of such optical transitions to a specific defect is not straightforward and several hypotheses have been raised in the literature.…”

“…While the latter can be associated with the FX excitation, the former is well above the values that are expected for the ZnO bandgap. One possible explanation for this blueshift is the presence of a high concentration of impurities in this sample, which can give rise to the Burstein-Moss effect, typically observed in heavily-doped materials, resulting in a band filling that shifts the optical bandgap for higher energies 21 , 76 , 77 . However, if that was the case, a blueshift of the UV PL emission should be also observed, in line with what is verified in the above mentioned situation 21 .…”

Electrochemical and Photoluminescence Response of Laser-induced Graphene/Electrodeposited ZnO Composites

“…The presence of broad bands in the visible spectral region is very frequent in ZnO crystals, both in bulk and in micro/nanostructures 55 . Indeed, the existence of orange/red luminescence bands has been widely reported in the literature 56,57 , especially in the case of low temperature synthesized materials 18 , and particularly in the ones prepared by electrodeposition 21,58,59 . The assignment of such optical transitions to a specific defect is not straightforward and several hypotheses have been raised in the literature.…”

“…While the latter can be associated with the FX excitation, the former is well above the values that are expected for the ZnO bandgap. One possible explanation for this blueshift is the presence of a high concentration of impurities in this sample, which can give rise to the Burstein-Moss effect, typically observed in heavily-doped materials, resulting in a band filling that shifts the optical bandgap for higher energies 21,74,75 . However, if this was the case, a blueshift of the UV PL emission should be also observed, in line with what is verified in the above mentioned situation 21 .…”

“…A yet unexplored synthesis approach is the pulsed electrodeposition of ZnO on LIG. A variety of ZnO morphologies can be obtained at low temperatures via this approach, in a versatile, cost-effective and scalable manner [19][20][21][22][23] .…”