The influence of Ce doping on the structural and optoelectronic properties of RF-sputtered ZnO films

Abstract

Using X-ray diffraction, UV-Visible spectroscopy, XPS and photoluminescence (PL) measurements, the structural, optical and electronic properties of ZnO and Cedoped ZnO thin films were investigated; the films were deposited on glass substrates by RF reactive-magnetron sputtering and post-annealed at 300 C in an oxygen atmosphere. Under similar deposition conditions, both films crystallized into hexagonal würzite lattice structures. The pure ZnO film exhibited a c-axis preferential orientation, whereas the Cedoped exhibited an a-axis preferential orientation. The films display uniform textured surfaces with columnar-like microstructures. The UV-Vis spectra showed high transparencies of 90 % on average for both films. Band gaps of E g ¼ 3:23 eV and E g ¼ 3:27 eV for pure and Ce-doped film, respectively, were measured. The doped film spectrum was shifted to the blue as a result of the Burstein-Moss effect. The XPS spectra show that the VB edge of the doped film shifts toward lower binding energy, at $ 1.3 eV below E F , while the VB edge of the pure film is located at $ 2.0 eV below E F . Additionally, Ce 3þ and Ce 4þ ions coexist in the ZnO matrix in fractions of $ 70 and $ 30 %, respectively. The PL spectra show that both types of ions induce extra electron states that allow multiple emission peaks in the blue-green region.

Strong near band edge emission of (Ce, Yb) co-doped ZnO thin films after high temperature annealing

“…Here, the improvement in crystal quality of the films should mainly be due to the high temperature annealing, but since the ratio is larger for the Ce and/or Yb doped films, it can be hypothesized that the RE ions can contribute to the improvement. It has been reported that Ce doping can contribute to a quality improvement [23,24,25]. Here the Ce doped film (S5) has the highest I NBE /I VIS ratio, and the Ce + Yb doped sample films (S1-4) have comparable I NBE /I VIS ratios, as predicted by the hypothesis.…”

“…Notably S5 has the highest ratios among the films at all the temperatures. Generally, the increase of the I NBE /I VIS ratio is often regarded to be due to the film crystal quality being improved [23], while some caution should be exercised in using that approximate general tendency to compare situations. Here, the improvement in crystal quality of the films should mainly be due to the high temperature annealing, but since the ratio is larger for the Ce and/or Yb doped films, it can be hypothesized that the RE ions can contribute to the improvement.…”

Origin of Visible Light Photoactivity of the CeO2/ZnO Heterojunction

“…Furthermore, the presence of ceria limits the growth of the ZnO phase, decreasing the crystallite size. The interaction between the two different phases (ZnO and CeO 2 ) and the formation of heterojunctions at boundaries limits the growth of the particles themselves . These assumptions were confirmed by TEM analysis in Figure where it is evident the difference in size between CeO 2 and ZnO particles.…”

Investigation of the annealing effects on the structural and optoelectronic properties of RF-sputtered ZnO films studied by the Drude–Lorentz model

“…The nonstoichiometry of films springs from loosely bound oxygen on the surface, other than lattice oxygen. Further details about conducted XPS analysis can be found elsewhere [19].…”