Band Gap Tuning in ZnO Through Ni Doping via Spray Pyrolysis

Abstract

The tuning of semiconductor band gaps can often provide significant performance increases and new applications for electronic, optoelectronic, and photocatalytic devices. Here, we study the band gaps of pure and nickeldoped zinc oxide thin films synthesized using the low-cost spray pyrolysis deposition method. Nickel concentration is varied from 0 to 15%, and the effects that this doping has on the electronic structure are analyzed. Using optical and synchrotron X-ray techniques, two regimes of band gap reduction via Ni doping are uncovered. For doping up to 4% Ni, there is a strong reduction in the gap, while continued doping up to 15% further reduces the gap, but to a lesser extent. The results are explained using X-ray spectroscopy and an Anderson impurity model. These tools show that the low doping case is driven by the interaction of the Ni 3d and O 2p states in both the valence and conduction bands. At high doping, the removal of Zn 3d states from the valence band and the change in Ni coordination from T d to O h both contribute to counteract the gap reduction. These results show how Ni can be used to tune the ZnO band gap over a large range useful for many applications.

X‐ray Absorption Spectroscopic Investigation of Ferromagnetic Ni‐doped ZnO

“…Additionally, there is a clear splitting of the L 2 region into two peaks, similar to the NiO spectrum. From Figure , we can say that the spectra of both the samples are best modeled by a Ni 2+ ion in octahedral coordination which is also supported by the results of theoretical simulations carried out by Das et al On the contrary, the Ni metal 2p XAS spectrum doesn't show a shoulder on the higher energy side of the L 3 peak and also the L 2 peak is a single peaked structure . It is noteworthy that the spectral line shapes of both the samples is completely different from that of the Ni metal as shown in figure 7 of Ref.…”

“…The large energy separation between these two arises due to spin‐orbit splitting of the 2p core holes. The spectra show a general shape typical of Ni 2+ (3d 8 ) compounds and quite similar to a NiO spectrum . For example, a strong shoulder is evident on the high‐energy side of the main L 3 peak (at ∼ 853.5 eV) in these spectra.…”

Tuning of material properties of ZnO thin films grown by plasma-enhanced atomic layer deposition at room temperature

“…5(d)] shows a rapid increase from 3.23 6 0.01 to 3.27 6 0.01 eV when increasing the RF-power from 30 to 40 W and then increases further to 3.28 6 0.02 eV for 150 W. This allows for bandgap tuning in a small range without the need for dopants, 54,55 applicable in a range of optical and electronic applications. The obtained value for the bandgap using Tauc fitting compares well with the literature; for example, Viezbicke et al 41 found an average value for the bandgap of 3.276 6 0.033 eV, comparing a large number of publications on thin film ZnO.…”

Effect of thickness on dielectric, ferroelectric, and optical properties of Ni substituted Pb(Zr0.2Ti0.8)O3 thin films

“…1,[8][9][10]18 The decrease of band gap by Ni-substitution in different materials has also been reported theoretically and experimentally by other research groups. [8][9][10]53,54 Here, the effect of thickness on E g is our central focus. A decrease was observed in direct-E g values from 4 eV to 3.4 eV and indirect-E g values from 3.5 eV to 2.9 eV as the thickness of the films increases from 5 nm to 400 nm.…”