Single Ionized Oxygen Vacancy Research Articles

Influence of crystal system, bond valence and ionic polarizability on the microwave dielectric properties of BaIn2O4 ceramic

BaIn2O4 ceramics with the monoclinic crystal system of the P21/c space group were synthesized using a solid-state reaction method. The sample sintered at 1250 °C exhibits a relative density (94.3 %) and the following microwave dielectric properties: εr = 16.3, Q × f = 49,500 GHz, τf = −73.1 ppm/°C. The bond valence results shows that the deviation of permittivity (24.9 %) between the experimental (εr = 16.3) and calculated values (εrC-M = 13.05) obtained using the Clausius−Mosotti equation may be ascribed to the rattling effect of Ba2+ and In3+. Compared with orthorhombic CaIn2O4 and SrIn2O4 ceramics, BaIn2O4 ceramics have lower Q × f values possibly because of the intrinsic loss caused by nonharmonic lattice vibration. The Edc value (0.43 eV) of BaIn2O4 demonstrates that the defects are caused by the single ionized oxygen vacancies. The intrinsic εr (14.7) and Q × f (105,600 GHz) values of the BaIn2O4 ceramic was inferred through infrared reflectivity spectroscopy. All results demonstrate that the dielectric properties are affected not only by density, ionic polarizability, and rattling effect of cations, but also by the crystal system, and particularly the intrinsic factors.

Gd3+ substitution effects, electrical and AC impedance characterizations of Gd/Cr co-doped SrBi4Ti4O15 Aurivillius-phase ceramics

Gd/Cr co-doped SrBi4Ti4O15 (Sr1-xGdxBi4Ti4O15 + 0.2 wt% Cr2O3, x = 0∼0.08) Aurivillius-phase ceramics were prepared by the traditional solid-state reaction process, the influences of Gd3+ doping concentration (x) on the structures and electrical properties of SrBi4Ti4O15 were investigated, as well as the AC impedance characterizations of the ceramics were analyzed. The incorporation of Gd2O3 and Cr2O3 into SrBi4Ti4O15 induced the lattice distortion of its orthorhombic structure. The donor substitution of Gd3+ for Sr2+ at A-site improved the Curie temperature (TC) and decrease the temperature coefficient of dielectric constant (TKε), as well as change the relaxation activation energy (Earel) of SrBi4Ti4O15 through the lattice distortion caused. Between 425 °C and 700 °C, the DC conduction behaviors of the ceramics was found with a transition from the mixed conduction mechanism involved in both the single-ionized oxygen vacancy and the double-ionized one to the single mode dominated by the latter one. Above TC, the imaginary part of modulus (M″) gradually shifts towards higher frequencies with increasing temperature, indicating the emergence of a new dielectric relaxation mode related to the phase transition process of the ceramics. Owing to the co-doping effects of Gd3+ and Cr3+, the optimized composition with x = 0.03 achieved excellent electrical properties (TC = 550 °C and d33 = 30 pC/N) and good thermal stability (TKε = 4.19 × 10−3/°C between RT and 500 °C, and the lose in d33 is only 3.3% after being annealed at 500 °C for 4 h), which make it promising for stable applications below 500 °C in the high-temperature piezoelectric devices.

Excited state absorption induced optical limiting behavior of pure, single, and co-doped copper oxide nanoparticles

Underneath nano pulsed green laser (Nd: YAG), nonlinear absorption and optical limiting behavior were analyzed using Z-scan technique for pure CuO, Ag, and Mn-doped CuO (single dopant), and Ag/Mn-doped CuO (co-dopant) nanoparticles intermediated from M. Oleifera leaf extract. X-ray diffraction pattern confirmed that the synthesized nanoparticles were in good crystalline nature with a monoclinic phase and the average crystallite size was estimated in the range of nanometer. FE-SEM analysis displayed that the pure CuO, Ag-doped CuO, and Ag/Mn-doped CuO appear as nanospheres whereas Mn-doped CuO forms themselves as nanorods. The existence of Cu, O, Ag, and Mn elements in synthesized nanoparticles was affirmed by an EDAX spectrum. FT-IR analysis confirms the presence of functional groups. In zeta potential analysis the negative (-ve) potential values −34.23 mV to −34.80 mV indicate the stability of the nanoparticles. The optical study revealed that the nanoparticles possess absorbance maxima in the UV region between 260 nm to 294 nm. The occurrence of a single ionized oxygen vacancy defect was affirmed by the photoluminescence studies. Z-scan studies with nano pulsed Nd: YAG lasers show all the samples exhibit two-photon absorption (2 PA) and optical limiting behavior. In contrast with pure and co-dopant materials (Ag/Mn-doped CuO), the dominant nonlinear absorption coefficients (0.90 × 10−10 m/W, & 0.98 × 10−10 m/W) and submissive values of optical limiting threshold (1.69 × 1012 W/m2 & 1.31 × 1012 W/m2) were found for single dopant materials (Ag & Mn-doped CuO). Thus single metal doped CuO finds potential application in the creation of laser safety devices against massive power nano pulsed green laser beams.

Energy storage, electrocaloric and optical property studies in Ho-modified NBT – BT lead-free ferroelectric ceramics

A comprehensive investigation of structural, microstructural, optical, electrocaloric, and energy storage properties of Ho-modified NBT-BT lead-free ceramics was conducted from room temperature to a high-temperature region. Rietveld refinement confirms the coexistence of dual-phase monoclinic (Cc) and tetragonal (P4mm) phases in Ho-modified NBT-BT ceramics. A prominent monoclinic distortion was found with increasing Ho composition up to x=0.02, and then an abrupt decrease for x=0.03 ceramic was noticed. Of particular importance is the composition of x = 0.02, which exhibits a high electrocaloric temperature change (ΔT) of 0.73 K @ E = 20 kV/cm at a temperature of 373 K, and an optimal high recoverable energy storage density (Wrec) of 1.8846 J/cm3 along with an efficiency 83% was achieved. The frequency dependence ac-conductivity study promotes the reduction of oxygen vacancies at room temperature and the dominance of single ionized oxygen vacancies at very high temperatures well above 300 °C. A small considerable increase in the energy bandgap values with the Ho3+ ion substitution in NBT-BT was observed. Under the excitation of 532 nm light, the two most prominent red fluorescence emission peaks were emitted, where the first emission band with weak intensity was observed at 657 nm which corresponds to the 5F5→5I8 transition, and a strong 2nd peak at 756 nm corresponds to the 5F4/5S2→5I7 level transition of the Ho3+ ion. These findings provide a feasible multifunctional property in the applications of power electronic devices with lead-free NBT-BT ceramics via rare-earth substitution.

Fortified relaxor ferroelectricity of rare earth substituted 4-layered BaBi3.9RE0.1Ti4O15 (RE = La, Pr, Nd, and Sm) Aurivillius compounds

In this report, the effect of rare-earth (RE3+) ion substitution on structural, microstructural, and electrical properties in barium bismuth titanate (BaBi4Ti4O15) (BBTO) Aurivillius ceramics has been investigated. The Rietveld refinements on X-ray diffraction (XRD) patterns confirm that all the samples have an orthorhombic crystal system with A21am space group. Meanwhile, temperature dependent synchrotron XRD patterns reveal that the existence of dual phase in higher temperature region. The randomly oriented plate-like grains are experimentally strived to confirm the distinctive feature of bismuth layered Aurivillius ceramics. The broad band dielectric spectroscopic investigation signifies a shifting of ferroelectric phase transition (Tm) towards low temperature region with a decrease of the RE3+-ionic radii in BBTO ceramics. The origin of diffuse ferroelectric phase transitions followed by stabilization of the relaxor ferroelectric nature at high frequency region is explained using suitable standard models. The temperature dependent ac and dc conductivity results indicate the presence of double ionized oxygen vacancies in BBTO ceramics, whereas the dominance of single ionized oxygen vacancies is observed in RE-substituted BBTO ceramics. The room temperature polarization vs. electric field (P–E) hysteresis loops are shown to be well-shaped symmetric for BBTO ceramics, whereas slim asymmetric ferroelectric characteristics developed at RE-substituted BBTO ceramics.

Effects of substitutional Fe and oxygen vacancies on room temperature ferromagnetism of Fe-doped In2O3 dilute magnetic nanowires

The magnetic behavior and origin of dilute magnetic nanowires are critical for further development and application of nanoscale spintronic devices. In this work, the Fe doping into single-crystalline In 2 O 3 nanowires are fabricated using chemical vapor deposition (CVD) method to research these problems based on theoretical and experimental analysis. The XRD, XPS, TEM and XAS results show that the deposited Fe-doped In 2 O 3 nanowires possess the cubic bixbyite structure and the doped Fe ions substitute for the In sites of In 2 O 3 lattice with +2 and + 3 mixed valences. The PL results prove the existence of single ionized oxygen vacancies as well as the defect complexes of donor (oxygen vacancy)-acceptor (Fe impurity) pairs. The intrinsic room temperature ferromagnetism can be observed for the Fe-doped In 2 O 3 nanowires and the saturation magnetization largely enhance with Fe doping. The first principles calculations show that the introducing of oxygen vacancy defects can cause strong hybridization between Fe 3d and O 2p orbitals at the Fermi level, resulting in the transition from antiferromagnetic to ferromagnetic coupling between the Fe ions. These results open up the possibilities for exploring spin-electronic devices. • Effects of Fe doping on local structure, optical and magnetic properties of Fe-doped In 2 O 3 nanowires are studied. • The doped Fe ions substitute for the In sites of In 2 O 3 lattice with +2 and + 3 mixed valences. • Single ionized oxygen vacancies and the defect complexes of donor -acceptor pairs can be observed. • Introducing of oxygen vacancies results in the transition from antiferromagnetic to ferromagnetic coupling between Fe ions.

Structural evolution, dielectric relaxation and modulus spectroscopic studies in Dy substituted NBT-BT ferroelectric ceramics

We report the effect of partial substitution of Dy3+ rare earth ion in NBT-BT lead free ceramics on its structural, microstructural, ferroelectric and dielectric phase transitions. The Rietveld refined X-ray diffraction analysis revealed a coexistence of dual phase with major monoclinic (Cc) along with minor tetragonal (P4mm) in all Dy-NBT-BT ceramics. The T-dependent dielectric broad band spectroscopic study revealed that Dy-substituted NBT-BT ceramics exhibits two diffuse dielectric anomalies renowned as Ferro (FE) to anti Ferro (AFE) i.e., depolarization phase transition ( $$T_{d}$$ ) and Antiferro (AFE) to paraelectric (PE) i.e., curie phase transition ( $$T_{C}$$ ), below 150 °C and well above 300 °C temperature regions respectively. The complex frequency dependent dielectric and modulus spectroscopy analysis supports the Non-Debye type dielectric relaxation process was dominated for all the measured ceramics. T-dependent AC-conductivity study revealed, thermally activated charge carries and single ionized oxygen vacancies are found to contribute conduction process at different temperature regions. Room temperature polarization hysteresis (P–E) loops analysis exposed a slim asymmetric shape with Dy substitution increasing that indicates conversion of hard to soft ferroelectric character. Remnant polarisation ( $$P_{r}$$ ) and coercive field ( $$E_{c}$$ ) decreases with dopant concentration shows the tetragonality dominance with Dy substitution. Furthermore, an optimum recoverable energy density 1.477 J/cm3 was obtained in NBT-BT at Dy = 0.03 compositions that designate the materials could be useful for future high energy storage density applications.

The effects of Sn–In co-doping on the structural, optical, photoluminescence and electrical characteristics of the sol-gel processed ZnO thin films

Abstract This work investigates the physical properties of sol-gel processed ZnO thin films under the influence of heterovalent Sn–In co-doping. Different characterization techniques were used to investigate the structural, optical, photoluminescence, and electrical properties of the films. All the films possess a hexagonal wurtzite structure of zinc oxide with preferred orientation along the (0 0 2) plane. As evident from the morphological images, all the films have a granular morphology with varying characteristics. In comparison to the undoped film, the optical transmittance of the 1TZO, 1T3IZO, and 3T1IZO films improves and is about ~80–85%. The direct energy bandgap of the films decreases upon co-doping due to the creation of energy states localized near the conduction band edge. The refractive index of the films varies between 3.36 and 1.69 in the wavelength range of 315–700 nm. The room temperature PL spectra of the films comprise one band-edge emission peak due to excitonic recombination in the UV region, and a broad emission peak associated with single ionized oxygen vacancies in the visible region. The 1T3IZO film shows the optimum transmittance and lower electrical resistivity.

Improved dielectric properties of Na1/2Y1/2Cu3Ti4O12 ceramics synthesized by ball-milling and reactive sintering

Na1/2Y1/2Cu3Ti4O12 (NYCTO) ceramics with giant dielectric constant (ε′) were synthesized by simple reactive sintering. NYCTO nanopowder was first synthesized using high energy ball-mill. Then the pelletized powder was sintered in air at temperatures in the range 975 °C to 1050 °C for 10–20 h. The obtained ceramics showed pure CaCu3Ti4O12 (CCTO)-like cubic phase as revealed by x-ray diffraction measurements. Field effect-SEM observations showed that the grain size increases from 2 μm to 5 μm with increasing sintering temperature. NYCTO samples sintered at temperatures higher than 975 °C showed giant dielectric constant (103–104) over most of the frequency range. The minimum dielectric loss (tanδ) of ∼0.055 at 300 K has been approved for the ceramic sample sintered at 1050 °C. Impedance and modulus spectra of the current samples showed two relaxations related to semiconductor (grain) and high resistance (grain-boundaries) elements. The activation energy for conduction located in the range 0.1–0.5 eV highlighted the role of single ionized oxygen vacancies in the dielectric properties of the investigated NYCTO ceramics.

Passivation Mechanism of Nitrogen in ZnO under Different Oxygen Ambience

Nitrogen-doped ZnO thin films were grown on a-plane Al2O3 by plasma-assisted molecular beam epitaxy. Hall-effect measurements indicated that the nitrogen-doped ZnO films showed p-type behavior first, then n-type, with the growth conditions changing from oxygen-radical-rich to oxygen-radical-deficient ambience, accompanied with the increase of the N/O ratio in the plasmas. The increasing green emission in the low temperature photoluminescence spectra, related to single ionized oxygen vacancy in ZnO, was ascribed to the decrease of active oxygen atoms in the precursor plasmas. CN complex, a donor defect with low formation energy, was demonstrated to be easily introduced into ZnO under O-radical-deficient ambience, which compensated the nitrogen-related acceptor, along with the oxygen vacancy.

XPS analysis of ZnO:Ga films deposited by magnetron sputtering: Substrate bias effect

This work focuses on X-ray photoelectron spectroscopy (XPS) and combined Raman and photoluminescence experiments performed on ∼500 nm thick ZnO:Ga films deposited by magnetron sputtering. The substrate bias voltage applied during the deposition was varied between 0 V (grounded) and −120 V in order to study the effect of Ga-doping on the ZnO wurtzite structure of the films and its electrical properties, when using a fixed doped composition of Ga2O3 (4.5 wt.%) in the ZnO sputtering target. XPS analysis revealed that ZnO dominates in all samples, while the Ga amount is the highest (∼2.9 at.%) for a substrate bias polarization of −60 V, diminishing substantially for either decreasing or increasing substrate polarizations. This increase in Ga concentration is responsible for the enhancement of electronic transport properties, resulting in a minimum electrical resistivity of ∼300 µΩ·cm. Moreover, the atomic layers closer to the surface are deficient in zinc for higher bias, due to the etching effect of Ar+ ions and subsequent Zn re-evaporation. From the Raman experiments, it was observed that the dynamics of the A1 and E1 phonons correlates with the decrease of the electrical resistivity. Photoluminescence studies revealed two broad bands, being one near the ZnO near-band-edge (3.4 eV) and another at higher energies (∼3.6 eV). The band centered at higher energies is more prominent for the case of the more electrically-conductive films, and is ascribed to electron transitions from the conduction band to single ionized oxygen vacancies. The lifetime of the polar-nature longitudinal optical phonons is in the range of 0.1–0.2 ps, which is quite small due to the Fröhlich interactions with gallium dopant atoms and other defects.

Broadband near-infrared downconversion luminescence in Yb3+-doped BaZn2(BO3)2

BaZn2(BO3)2 self-activated phosphors were prepared by the conventional high temperature solid-state method. The PL spectra of BaZn2(BO3)2 powders prepared under reductive and air atmosphere consist of a weak ultraviolet emission band (∼410 nm) and a broad emission band which were centered at ∼ 500 and 545 nm, respectively. According to the spectral analysis and EPR results, the green and yellow emissions may arise from the transitions of photo-generated electron close to the conduction band to the deeply trapped hole in single ionized oxygen vacancy (V+ o) centers and single negatively charged interstitial oxygen ion (O- i), respectively. An efficient broadband near-infrared (NIR) quantum cutting was demonstrated in Yb3+ doped BaZn2(BO3)2 phosphor. Upon excitation with an ultraviolet photon at 375 nm, the emissions of two NIR photons at 983 nm from Yb3+ ions were achieved. The dependences of the visible and NIR emissions, the decay lifetime, the energy transfer efficiency, and the quantum efficiency on the Yb3+ doping content were investigated in detail. The results indicated that the maximum energy transfer and the corresponding downconversion quantum efficiency could reach between 68.5% and 168.5%.

Conduction mechanism and magnetic behavior of Cu doped barium hexaferrite ceramics

M-type barium hexaferrite ceramics (BaM) are important materials owing to their tremendous applications and useful properties. However magnetic and electrical properties of Cu substituted BaM haven’t been studied yet. In the present study, Cu doped BaM samples having chemical formula BaFe12−xCuxO19 (where x = 0, 0.1, 0.3 and 0.5) were synthesized by conventional solid state mixed oxide route. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the formation of hexagonal magnetoplumbite structure with space group P63/mmc as the major phase in all the samples. Scanning electron microscopy revealed the dense structure of undoped and doped samples with platelet-like morphology. Vibrating sample magnetometry showed a large decrease in the coercivity of BaM without the loss of saturation magnetization by the addition of Cu. Magnetic measurement at cryogenic temperature (25 K) revealed that Cu doped sample showed less variation in magnetic properties on decreasing the temperature as compared to undoped BaM samples. Room temperature dielectric studies showed that addition of Cu caused a decrease in dielectric loss however it increased at higher substitution level i.e. x = 0.5. High temperature conductivity studies revealed that single-ionized oxygen vacancies are responsible for conduction in Cu doped BaM.

Enhancing the performance of room temperature ZnO microwire gas sensor through a combined technology of surface etching and UV illumination

Enhancing the performance of individual micro/nanowires based room temperature gas sensors is a big challenge for real-time detection of toxic gases. In this work, we developed a surface etching method to increase the sensitivity of individual ZnO microwire (MW) based gas sensor. The etching of the MW increases the adsorption sites for gas molecules on it by increasing the specific surface area and the surface density of single ionized oxygen vacancies. This leads to a ∼20-fold increase of the gas sensor’s sensitivity. When working under 148.8 μW cm−2 of UV light, the sensitivity is further increased to 411%. Meanwhile, the response and the recovery time decreases to ∼20% and ∼2% of the values in dark condition, respectively. As a result, the individual ZnO microwire based gas sensor’s performance was greatly enhanced, and it has great potential to be used as a room temperature gas sensor towards NO2.

Investigation of some physical properties of ZnO nanofilms synthesized by micro-droplet technique

In this paper, ZnO nanocrystals were synthesized using a simple micro-droplets technique from a solution prepared by dissolving zinc acetate di-hydrate [Zn(CH3COO)2, 2H2O] in methanol. Microdroplets were deposited on glass substrates heated at 100°C, the obtained samples of ZnO films were investigated by XRD, AES, AFM, ellipsometry and PL. XRD patterns reveal the wurtzite structure of ZnO where the lattice parameters a and c, calculated from XRD signals, show a nanometric character of ZnO nanoparticles. The chemical composition of ZnO film surfaces was verified by Auger electron spectroscopy (AES). From Auger signals, oxygen (O-KLL) and zinc (Zn-LMM) Auger transitions indicate well the presence of Zn-O bonding. The surface topography of the samples was measured by atomic force microscopy (AFM) where ZnO nanoparticles of average size ranging between 20 and 80nm were determined. Some optical properties as dielectric constants, refractive index, extinction coefficient as well as the optical band gap were determined from ellipsometry analysis. The dispersion of the refractive index was discussed in terms of both Cauchy parameters and Wemple & Di-Dominico single oscillator model. The photoluminescence (PL) measurements exhibited two emission peaks. The first at 338nm, corresponding to the band gap of ZnO, is due to excitonic emission while the second around 400nm, is attributed to the single ionized oxygen vacancies.

Effect of surface-to-volume ratio on the optical and magnetic properties of ZnO nanorods by hydrothermal method

ZnO nanorods have been fabricated by hydrothermal method with different precursor concentrations. The structural, optical and magnetic properties of ZnO nanorods have been investigated. With the precursor concentration increase, the surface-to-volume ratio of ZnO nanorods decreases. Photoluminescence (PL) spectra of all samples are dominated by the visible emission band related to the defects. PL spectra under different excitation energies and PL excitation (PLE) spectra revealed that yellow-green emission band is related to a transition from a shallow donor level to doubly ionized oxygen vacancy (Vo2+) and green emission band to the recombination of electrons trapped in single ionized oxygen vacancies (Vo+) with photo-generated holes. With the precursor concentration increase, the decrease of surface-adsorbed O2 and OH− species, as acceptor and donor surface states, induces the reduced non-radiative transition probabilities and enhanced yellow-green emission band. The reduction of room temperature ferromagnetism was observed with the decrease of surface-to-volume ratio of ZnO nanorods.

Defect based violet–blue emission of Mg doped ZnO annealed at different temperatures

This paper describes structural and optical characterization of Mg doped ZnO nanoparticles. The system Zn1−xMgxO with x = 0.0, 0.01, 0.03, 0.05, 0.1 were prepared by a simple chemical method and annealing at different temperatures, T = 500, 700 and 900 °C. XRD spectra and the Rietveld refinement show that the crystalline phase of these samples belongs to the wurtzite hexagonal structure of space group P63mc. The PL results show three main emission bands in the violet and blue emission regions. The presence of several emission bands are attributed to free excitation transitions, interstitial Zn, local zinc vacancy, single ionized oxygen vacancy, and deep level emissions. PL studies at 500 °C revealed that visible PL emission was enhanced with doping concentration (x). Mg doped ZnO structures have changed the optical properties significantly.

Unexpected ferromagnetism in Ist group elements doped ZnO based DMS nanoparticles

Undoped and Ist group elements (Li+, Na+, and K+) doped ZnO nanoparticles (NPs) were prepared by a co-precipitation method. Both undoped and Ist group elements doped ZnO NPs exhibit ferromagnetic behavior at room temperature which is analyzed by a vibrating sample magnetometer (VSM). Furthermore, the Ist group elements doped ZnO NPs enhance the ferromagnetic nature of ZnO compared with pure ZnO NPs. Further, the crystalline phase, local structure and optical analysis were done by X-ray diffraction (XRD), Raman spectroscopy and photoluminescence (PL) analysis to examine the undoped and Ist group elements doped ZnO NPs. From our results and analysis, the observed ferromagnetism and its enhancement are radically due to the single ionized oxygen vacancy (V+o) and acceptor dopants.

Growth and characterization of Mn-doped In2O3 nanowires and terraced microstructures

Mn-doped In2O3 micro- and nanostructures were grown by the thermal evaporation–deposition method using a precursor powder composed of In2O3 and a manganese compound. Terraced microstructures grow at 1200°C when using Mn2O3 in the precursor powders, while thinner micro- and nanowires have been obtained at temperatures between 560 and 780°C by using MnCO3 in the precursor mixture. The morphology, as well as the luminescencent, electrical and chemical properties, of the Mn-doped In2O3 micro- and nanostructures were characterized by means of X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, cathodoluminescence (CL), energy dispersive X-ray spectroscopy, remote electron beam induced current (REBIC) and X-ray photoelectron spectroscopy (XPS). The amount of Mn incorporated in these low-dimensional structures is below 1at.%. The Mn-doped In2O3 structures show luminescence at 1.91 and 2.27eV, related to defects associated with an excess of oxygen and single ionized oxygen vacancies (VO+), respectively. An emission at 2.94eV, possibly due to the direct band gap of In2O3, has been also observed. The presence of VO+, which tend to accumulate at the edges of the terraces of the microstructures, has been traced by combined CL–REBIC–XPS techniques, and has been related to the incorporation of manganese as Mn2+.

Defect reduction in photon-accelerated negative bias instability of InGaZnO thin-film transistors by high-pressure water vapor annealing

We investigated the effects of high-pressure water vapor annealing (WHPA) under negative bias temperature illumination stress and light incidence on amorphous InGaZnO thin-film transistors. WHPA could improve device reliability and reduce the hump occurrence. It was attributed to the effective reduction and passivation in oxygen vacancies under WHPA. By comparing the experimental and technology computer-aided design simulation, we could confirm that the low-density of deep-donor-like oxygen vacancy (Vo) states near the valance band maximum contributed to the reduction of photo-excited single ionized oxygen vacancies (Vo+) and double ionized oxygen vacancies (Vo2+) as shallow-donor states near the conduction band minimum.