Investigation of the Changes in Electronic Properties of Nickel Oxide (NiO_x) Due to UV/Ozone Treatment

Abstract

Drastic reduction in nickel oxide (NiO) film resistivity and ionization potential is observed when subjected to ultraviolet (UV)/ozone (O) treatment. X-ray photoemission spectroscopy suggests that UV/O treatment changes the film stoichiometry by introducing Ni vacancy defects. Oxygen-rich NiO having Ni vacancy defects behaves as a p-type semiconductor. Therefore, in this work, a simple and effective technique to introduce doping in NiO is shown. Angle-resolved XPS reveals that the effect of UV/O treatment does not only alter the film surface property but also introduces oxygen-rich stoichiometry throughout the depth of the film. Finally, simple metal/interlayer/semiconductor (MIS) contacts are fabricated on p-type Si using NiO as the interlayer and different metals. Significant barrier height reduction is observed with respect to the control sample following UV/O treatment, which is in agreement with the observed reduction in film resistivity. From an energy band diagram point of view, the introduction of the UV/O treatment changes the defect state distribution, resulting in a change in the pinning of the Fermi level. Therefore, this work also shows that the Fermi level pinning property of NiO can be controlled using UV/O treatment.

Efficient Inverted Planar Perovskite Solar Cells Using Ultraviolet/Ozone‐Treated NiOx as the Hole Transport Layer

“…The conductivities are estimated to be 1.99 × 10 −6 S cm −1 (0 min), 2.19 × 10 −6 S cm −1 (1 min), 2.89 × 10 −6 S cm −1 (5 min), 3.00 × 10 −6 S cm −1 (10 min), and 3.01 × 10 −6 S cm −1 (20 min), respectively. This result is roughly consistent with the previous literature, in which the electrical conductivity rose to more than one order of magnitude higher after the NiO x film was treated by UVO for 10 min. Furthermore, we have derived the optical bandgap of the samples from the Tauc plots in Figure d, in which (αhν) 2 is plotted as a function of hν from previous absorption spectra, with α, h, and ν representing the absorption coefficient, Planck constant, and light frequency, respectively.…”

“…Comparing the XPS spectra of the NiO x under different conditions together, we find that Ni 3+ state has been gradually outnumbering the Ni 2+ state with increasing time (can be found in Figure S4a in the supporting information). This change has clearly indicated a continuous stoichiometry (O/Ni ratio) transformation versus time (Figure S4b, Supporting Information), which is consistent with the formation of Ni vacancies . More importantly, it has also indicated the significant controllability of the x value in the NiO x by the UVO treatment.…”

“…Secondly, high energy photons could also influence the oxidization state and crystalline situation in the oxides . Therefore the chemical and microstructural properties of the objects have been further investigated, as shown in Figure .…”

Investigation on tailoring physical properties of Nickel Oxide thin films grown by dc magnetron sputtering

“…The characteristic core level O1s peak located at 529.16 to 529.27 eV is ascribed to Ni +2 because of lattice oxygen interaction in the form of Ni-O octahedral bonding of NiO [37]. The peak at 530.83 to 531 eV represent the Ni +3 which indicate vacancy or metal deficiency in the films and a small peak located at ∼531.90 to 532.10 eV represents the O-H group and 533.26 eV represents the adsorbed O 2 element present in the deposited NiO surface layer [11,38]. The oxidation state of Ni +2 peak position is slightly shifted from 529.16 to 529.27 eV with increase in the oxygen partial pressure from 5 to 10 sccm during the deposition.…”

High‐Performance Quantum‐Dot Light‐Emitting Diodes Using NiOx Hole‐Injection Layers with a High and Stable Work Function

“…In general, the work functions of the pristine solution‐processed oxide films are lower than 5.2 eV, which cannot form low‐resistance contact with the organic HTLs with high ionization potentials . A few postdeposition treatments, such as ozone treatment and oxygen‐plasma treatment, were applied to increase the work function of the oxide HILs . However, as shown below, the work functions of oxide HILs after ozone treatment can be unstable, which may degrade the operational lifetime of the QLEDs.…”