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3D atomic structure of initial Li-X doped ZnO (LXZO) geometries. Grey (red) balls indicate Zn (O) atoms. Labels Li and X and correspondingly light grey and blue spheres identify the different dopant chemical species. V O and V Zn hosts are obtained by removing the atoms marked by the circle and the star, respectively; V dim host results from the removal of both atoms.
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We report on first principle investigations about the electrical character of Li-X codoped ZnO transparent conductive oxides (TCOs). We studied a set of possible X codopants including either unintentional dopants typically present in the system (e.g., H, O) or monovalent acceptor groups, based on nitrogen and halogens (F, Cl, I). The interplay betw...
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Context 1
... we can realistically assume that the undoped ZnO samples intrinsically include structural defects, such as vacancies and dislocations, whose amount strictly depends on the growth techniques. In order to decouple the complex interplay between the existing defects and the dopants, we considered four possible initial hosts each including zero (ideal ZnO crystal) or one neutral point defect, namely: an oxygen (V O ), a zinc (V Zn ), and a Zn-O dimer (V dim ) vacancy, as shown in Figure 1. All defective ZnO structures were fully relaxed to the minimum energy configurations. ...
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... initial geometry for each LXZO system has been obtained including an Li atom and a X codopant in interstitial positions with respect to the crystalline host, which may include a relaxed point defect in the structure ( Figure 1). Every LXZO system has been first heated to room temperature for 1.5 ps (via ab initio molecular dynamic simulations), and then relaxed to the ground state at T = 0 K. Finally, the DFT+U (see Section 4) electronic structure has been collected for the optimized samples. ...
Context 3
... system is simulated in an orthorombic periodic supercell of size (13.15 × 11.39 × 10.63) Å 3 , which includes 32 unit cells of wurtzite ZnO (i.e., 128 atoms), one Li-X impurity (Li, Li 2 , LiH, Li-OH, Li-LiO, Li-N, Li-NH 2 , Li-NO 2 , Li-CN, Li-F, Li-Cl, Li-I) and-depending on the system-a structural point defect, namely, an oxygen (V O ), a zinc (V Zn ) or a Zn-O dimer (V dim ) vacancy (Figure 1). In order to sample the chemical environment felt by the Li compounds in the ZnO matrix, each system undergoes a cycle of annealing to 300 K for 1.5 ps. ...
Citations
... The oxides of the p block elements were opted to dope so that the doping will activate the hole-pair movements during photo catalysis of ZnO [5][6][7][8][9] . ZnO doped with selenium also have photoelectronic properties and contribute to the crystallite size [10][11] . ...
Metal oxide nanoparticles have taken a broad area of intense research because of their unique properties and application in diversified fields. Zinc oxide (ZnO) nanoparticles show varied morphologies and significant activities especially after doped with different metals. In this work, ZnO nanoparticles, Selenium dioxide (SeO2) doped Zinc oxide nanoparticles and Silicon dioxide (SiO2) doped Zinc oxide nanoparticles are synthesised by sol-gel method. The dopant effect on ZnO for band gap energy, crystal size and morphology are investigated by analysing the UV-DRS, powder X-ray diffraction and FESEM measurements respectively. The photocatalytic activities of these synthesised nanoparticles are compared by subjecting them into degradation of drug Lasix (furosemide) under UV and Solar irradiation sources. The progress of drug degradation is studied by measuring absorbance versus time interval at constant wavelength (325 nm) of the drug. The rate coefficient values found in this oxidative (H2O2) and reductive (NaBH4) catalytic degradation process of the drug is found efficient in solar irradiations. The results of characterisation studies and the order of photocatalytic activities of the nanoparticles are discussed.
... A large number of scientific studies devoted to investigation of the properties of zinc oxide were carried out in recent years [1][2][3][4][5][6][7][8]. Zinc oxide is interesting as a direct-gap semiconductor widespread in nature having a band gap of 3.36 eV. ...
... It is known that in the presence of a uniform electric field, the ionization potential of atoms of a solid decreases by Δϕ P-F . The dependence of the conductivity σ on the electric-field strength E is described by the relation (8) where is the conductivity in weak fields, W g is the band gap, and N C is the effective density of states in the conduction band. An external electric field through the Poole-Frenkel effect increases the probability of the ejection of electrons captured in traps contained in dielectrics and having a Coulomb-type barrier. ...
The results of an experimental study of the surface morphology of zinc-oxide films and the electrical properties of structures based on a single-crystal Si/microcrystalline ZnO heterojunction are presented. An analysis of the structure of the zinc-oxide films grown in argon and oxygen atmospheres is carried out, and the size distribution of nanofibers grown on its surface is obtained. The capacitance–voltage characteristics of In/ZnO/n-Si/Al and Au/ZnO/n-Si/Al heterostructures are simulated. On the basis of calculations and comparison of the experimental and simulated dependences, the concentration of free charge carriers in the sample and the position of the Fermi level are determined, the presence of a fixed charge in the system is revealed, and the density of surface states is found based on the ratio of the voltage applied to the system and the surface potential at the interface between layers. The value of the built-in surface charge is calculated. The relationship between the material of the upper contacts and the capacitance–voltage and current–voltage characteristics of the system is studied. The resistance of the formed zinc-oxide films is alculated. The prevailing charge-transfer mechanisms are discussed. An empirical dependence of the surface potential of silicon on the voltage applied to the structure is revealed. The effect of technological modes for obtaining zinc-oxide films synthesized by spray pyrolysis on the surface structure, effective capacitance of the structure, density of electronic states, and processes of charge-carrier transfer in samples under the action of an electric field is analyzed.
... For example, when Mg occupies the Ga atomic site in GaN, it acts as a p-type dopant, while in the interstitial site, it behaves as an n-dopant. 7,8 Similar observations were also made on the Li doping in ZnO 9 and other examples of amphoteric dopants. 10,11 Therefore, from a device application point of view, controlling the types and nature of point defects as well as their concentrations is extremely important for achieving optimum performance, and careful experiments and meticulous modeling analysis are required to understand the complete nature of various kinds of defects and their impacts on the physical properties of materials. ...
Point defects create exotic properties in materials such as defect-induced luminescence in wide-bandgap semiconductors, magnetism in nonmagnetic materials, single-photon emission from semiconductors, etc. In this article, oxygen defect formation in metallic TiN and semiconducting rock salt-(Al,Sc)N is investigated with a combination of first-principles density functional theory, synchrotron-based x-ray absorption spectroscopy (XAS) analysis, and scanning transmission electron microscopy–energy-dispersive x-ray spectroscopy mapping. Modeling results show that oxygen in TiN and rock salt-(Al,Sc)N prefers to be in the defect complex of substitutional and interstitial oxygen (nON + Oi) types. While in TiN, the preferential interstitial sites of oxygen in ON + Oi are at the tetrahedral site, in rock salt-(Al,Sc)N, a split interstitial site along the [111] direction was found to be energetically preferable. Simulations performed as a function of the oxygen partial pressure show that under experimental growth conditions, four oxygen atoms at the substitutional sites of nitrogen (4ON), along with four Ti atoms, decorate around an interstitial oxygen atom at the tetrahedral site (Oi) in the energetically favored configuration. However, in rock salt-(Al,Sc)N, n in nON + Oi was found to vary from two to four depending on the oxygen partial pressure. Theoretical predictions agree well with the experimentally obtained XAS results. These results are not only important for a fundamental understanding of oxygen impurity defect behavior in rock salt nitride materials but will also help in the development of epitaxial metal/semiconductor superlattices with efficient thermionic properties.
... [188][189][190][191] Analogously, Li doped ZnO (≈3.6 eV) has a p-type character, when Li is included as Zn substitutional dopant, but it turns into an n-type when Li is in interstitial sites. [192,193] In complex oxides, the concept of chemical modulation of the valence band (introduced by Kawazoe, Hosono et al. [194] in 1997) is a well-known route to reduce the p-type oxide resistivity of Cu-based ternary compounds. The acceptor conductivity in these complex oxides increases due to the formation of tight covalent bindings and the hybridization of O 2p and (closed shell) Cu 3d 10 orbitals. ...
New device concepts and new computing principles are needed to balance our ever‐growing appetite for data and information with the realization of the goals of increased energy efficiency, reduction in CO2 emissions, and the circular economy. Neuromorphic or synaptic electronics is an emerging field of research aiming to overcome the current computer's Von‐Neumann bottleneck by building artificial neuronal systems to mimic the extremely energy efficient biological synapses. The introduction of photovoltaic and/or photonic aspects into these neuromorphic architectures will produce self‐powered adaptive electronics but may also open new possibilities in artificial neuroscience, artificial neural communications, sensing, and machine learning which would enable, in turn, a new era for computational systems owing to the possibility of attaining high bandwidths with much reduced power consumption. This perspective is focused on recent progress in the implementation of functional oxide thin‐films into photovoltaic and neuromorphic applications toward the envisioned goal of self‐powered photovoltaic neuromorphic systems or a solar brain.
... In search of acceptor dopants in ZnO, perhaps the most attempted elements are Li and N [1][2][3][4][5]. Even after so many reports, the configuration of Li and N in ZnO is still a matter of debate [6,7]. ...
... Earlier studies on Ga,N and Al,N codoped ZnO samples have indicated [6,19] that the presence of I Zn related donors hinder effective acceptor activation through N chemical states. In turn, doping Mg [20], P [21], Li [1] along with N can be effective for reducing I Zn related donors. In fact, strong Electroluminescence (EL) emissions have been observed in Li and N dual doped ZnO around 415 nm and 500 nm at room temperature leading to successfully fabrication of light-emitting diodes (LEDs) [5]. ...
Doping lithium (Li) and/or nitrogen (N) in ZnO and activation of shallow acceptors thereby have drawn specific scientific interest for the last few years. A comprehensive study employing Raman spectroscopy is being reported here on N and Li implantation effects in ZnO. Strong presence of 275 cm⁻¹ Raman mode after N and (Li,N) implantation confirms its relation with doped nitrogen in ZnO. Weak presence of 510 cm⁻¹ mode in the high fluence implanted ZnO indicates its origin with interstitial defects. No extra Raman mode has been identified in Li implanted samples. Raman mode with anomalously large intensity is found at 1562 cm⁻¹ after (Li,N) co-implantation (highest fluence). Implantation causes huge increase of Raman modes ~ 540, 555 and 579 cm⁻¹, with the last two bearing clear co-relations with interstitial Zn and O vacancy, respectively. To identify shallow acceptors due to dopant-defect complex, low temperature photoluminescence (PL) has been monitored but only donor related excitonic features are visible in the near band edge (NBE) emission. However, indications in favour of deep acceptors states are noted, particularly when Li is present in the sample. The deep acceptor level may be at~ 300 meV above the valence band consistent with previous results.
... At variance with Al, which is a degenerate dopant, it must be noted that the observed p-conductivity derives from the only partial saturation by copper of the charge depletion associated to the substituted Zn atom. This is reflected by the Fermi level pinning at defect states, as revealed by the comparison of DOS for different Cu contents reported in Fig. 3. Similarly, the net magnetization is associated to unpairing of neighboring S-orbitals induced by the partially saturated Zn vacancies, as it happens for the case of ZnO [39][40][41] . ...
We revise the electronic and optical properties of ZnS on the basis of first principles simulations, in view of novel routes for optoelectronic and photonic devices, such as transparent conductors and plasmonic applications. In particular, we consider doping effects, as induced by Al and Cu. It is shown that doping ZnS with Al imparts a n-character and allows for a plasmonic activity in the mid-IR that can be exploited for IR metamaterials, while Cu doping induces a spin dependent p-type character to the ZnS host, opening the way to the engineering of transparent p-n junctions, p-type transparent conductive materials and spintronic applications. The possibility of promoting the wurtzite lattice, presenting a different symmetry with respect to the most stable and common zincblende structure, is explored. Homo- and heterojunctions to twin ZnO are discussed as a possible route to transparent metamaterial devices for communications and energy.
The results of an experimental study of the surface morphology of zinc oxide films and the electrical properties of structures based on the monocrystalline Si/microcrystalline ZnO heterojunction are presented. The structure of zinc oxide films grown in an atmosphere of argon and oxygen is analyzed, and the size distribution of nanoscale fibers grown on its surface is obtained. The capacitance-voltage characteristics of the In/ZnO/n-Si/Al and Au/ ZnO/n-Si/Al heterostructures have been simulated. Based on the calculations and comparison of experimental and model dependences, the concentration of free charge carriers in the sample and the position of the Fermi level were determined, the presence of a fixed charge in the structure was revealed, the density of surface states was found based on the ratio of the voltage applied to the structure and the surface potential at the interface of the materials of the layers of structures. The value of the built-in surface charge is calculated. The interrelation of the upper contact material with the volt-farad and volt-ampere characteristics of the structure is investigated. The resistance of the formed zinc oxide films is calculated. The prevailing charge transfer mechanisms are discussed. The influence of technological modes of obtaining zinc oxide films obtained by spray pyrolysis on the structure of the surface, the effective capacity of the structure, the density of electronic states, the processes of charge carrier transfer in samples under the action of an electric field is analyzed.
This study aims to assess structural, optical, and electrical properties of AZO thin films produced by magnetron sputtering in high pressure were 12, 7, and 5 cm apart between the target and the glass substrate. Then, a treatment current variation (0.1, 0.2, and 0.3 A) was performed for the fixed position of 5.0 cm away. Characterization techniques such as XRD, SEM, and EDS were used to investigate the structural changes and composition of the deposited films. Besides, spectrophotometry enabled an analysis of the optical constants, and the four-point probe assay was used to measure the film electrical resistance. The results showed that the approximation between the target/substrate, and the increase in current from 0.1 to 0.3 A, produces an increase in crystallinity, grain size, and film thickness. These factors promote a reduction in transmittance, bandgap energy, and electrical resistivity. Sample A503 (5.0 cm and 0.3 A) showed the best electrical properties (2.18 x 101 Ω.cm) in view of the set of parameters adopted in this work.
First-principle calculations were performed to investigate the electronic structure, optical, and ferromagnetic properties of Ag/Co single- and co-doped ZnO. We found that both ZnO single-doped Ag and co-doped Ag/Co exhibit room-temperature ferromagnetism, whereas ZnO single-doped Co shows anti-ferromagnetism. Strongly enhanced room temperature ferromagnetism with saturate magnetization of 10.45 μB has been obtained in ZnO co-doped with Ag/Co, making it a promising room temperature ferromagnetic material. The magnetic moments of Ag/Co co-doped ZnO are mainly derived from the double-exchange effect between Co-3d state and O-2p state, which is consistent with Ruderman–Kittel–Kasuya–Yosida double exchange mechanism theory. In addition, Ag-doped ZnO undergoes a transition from magnetic to non-magnetic with the Ag doping concentration increasing from 2.77 mol% to 5.55 mol%. Ag/Co single- and co-doping can remarkly enhance absorption in the visible range. However, Ag single-doped ZnO has a long carrier lifetime and is conducive to the experimental design and preparation of new photocatalysts. Further research found that the interstitial hydrogen can induce the generation of magnetic order, reduce the magnetic moments and enhance the photocatalytic ability.
The impact of hydrogen in ZnO is revealed by combining reaction dynamics calculations with temperature dependent Hall (TDH), photoluminescence, and secondary ion mass spectrometry measurements performed on H, 2H, and He implanted ZnO. H and 2H box profiles with a concentration ranging from ∼3×1017 cm−3 to ∼1019 cm−3 and He to produce as much as damage as in the [H] ∼3×1017 cm−3 case were implanted in the samples. The formation of Li lean regions has been observed for [2H] <1019 cm−3 after annealing at 400 °C. This is attributed to Lii presence consequent to the diffusion of Zni created during the H/2H implantation process. Results extracted from the TDH measurements performed prior to the annealing at 400 °C evidence that Lii contributes to an increase in carrier concentration up to ∼1017 cm−3 by providing a donor level with an activation energy of ∼40 meV and thus is very close to the value of ∼47 meV expected for H in the oxygen site. The reaction dynamics analysis evidences that the amount of Lii introduced is decreasing at higher H implantation doses as a result of increasing VZn and H-VZn retrapping, reactions in which Lii is competing with H. Overall, due to Lii formation as well as the presence of Al the maximum percentage of the implanted H or 2H acting as a donor in the investigated range is found to be ≲ 2%, which is considerably lower than previously reported.
