Effect Of Native Defects Research Articles

First-principles studies on cation point defects in LiTi2O4

Lattice defects are common in electrode materials and may affect their structural stability and electrochemical performance. Here we use first-principles calculations based on density functional theory to investigate native cation point defects in spinel LiTi2O4, a potential candidate for anode material in lithium ion batteries. We consider vacancies, interstitials, antisite defects, Frenkel defects and some defect pairs. Our calculations show that Li interstitial, Ti interstitial, Li Frenkel defect and Li antisite are low-energy defects, and thus they would be detectable in LiTi2O4, while cation vacancies and Ti Frenkel defect are hard to form due to their high formation energy. Binding energies are calculated to illustrate whether the isolated defects will clustering or not. In addition, the effect of native defects on migration of Li is studied. We find that Li antisites can make the migration barrier of Li interstitial decreasing significantly.

Anomalies in the bulk and surface electronic properties of SnS: effects of native defects

A combinatorial approach of experiment and theory was used to investigate the defect induced bulk and surface electrical properties of SnS.

First-principles study of defects at [formula omitted] grain boundaries in CuGaSe[formula omitted

We present a first-principles computational study of cation–Se Σ3 (112) grain boundaries in CuGaSe2. We discuss the structure of these grain boundaries, as well as the effect of native defects and Na impurities on their electronic properties. The formation energies show that the defects will tend to form preferentially at the grain boundaries, rather than in the grain interiors. We find that in Ga-rich growth conditions Cu vacancies as well as Ga at Cu and Cu at Ga antisites are mainly responsible for having the equilibrium Fermi level pinned toward the middle of the gap, resulting in carrier depletion. The Na at Cu impurity in its +1 charge state contributes to this. In Ga-poor growth conditions, on the other hand, the formation energies of Cu vacancies and Ga at Cu antisites are comparatively too high for any significant influence on carrier density or on the equilibrium Fermi level position. Thus, under these conditions, the Cu at Ga antisites give rise to a p-type grain boundary. Also, their formation energy is lower than the formation energy of Na at Cu impurities. Thus, the latter will fail to act as a hole barrier preventing recombination at the grain boundary, in contrast to what occurs in CuInSe2 grain boundaries. We also discuss the effect of the defects on the electronic properties of bulk CuGaSe2, which we assume reflect the properties of the grain interiors.

Effect of native defects on thermoelectric properties of copper iodide films

Effect of native defects on thermoelectric properties of copper iodide films

Design and Analysis of Gallium Nitride-Based p-i-n Diode Structure for Betavoltaic Cell with Enhanced Output Power Density.

In this work, Gallium Nitride (GaN)-based p-i-n diodes were designed using a computer aided design (TCAD) simulator for realizing a betavoltaic (BV) cell with a high output power density (Pout). The short-circuit current density (JSC) and open-circuit voltage (VOC) of the 17 keV electron-beam (e-beam)-irradiated diode were evaluated with the variations of design parameters, such as the height and doping concentration of the intrinsic GaN region (Hi-GaN and Di-GaN), which influenced the depletion width in the i-GaN region. A high Hi-GaN and a low Di-GaN improved the Pout because of the enhancement of absorption and conversion efficiency. The device with the Hi-GaN of 700 nm and Di-GaN of 1 × 1016 cm−3 exhibited the highest Pout. In addition, the effects of native defects in the GaN material on the performances were investigated. While the reverse current characteristics were mainly unaffected by donor-like trap states like N vacancies, the Ga vacancies-induced acceptor-like traps significantly decreased the JSC and VOC due to an increase in recombination rate. As a result, the device with a high acceptor-like trap density dramatically degenerated the Pout. Therefore, growth of the high quality i-GaN with low acceptor-like traps is important for an enhanced Pout in BV cell.

Role of Native Defect in Near Room Temperature CH4 Sensing Using Nanostructured V2O5

Native defects are highly prevalent in vanadium pentoxide (V2O5) as it can easily get converted into reduced oxides. The role of defects in gas sensing properties of V2O5 nanostructures, however, are not well understood. In the present report, effect of native defects on near room temperature sensing is reported for the first time. Hydrothermally grown V2O5 nanoparticles with substantial sensor response to CH4 close to room temperature at 50 °C is presented. Fast response and recovery times of 43 s and 75 s, respectively, for 500 ppm CH4 gas at optimum operating temperature of 150 °C were observed. Temperature dependent photoluminescence studies were carried out to understand the role of native defects and their emission behavior leading to carrier saturation in realizing optimum operating temperature.

Designing an active Ta3N5 photocatalyst for H2 and O2 evolution reactions by specific exposed facet engineering: a first-principles study.

The effects of native defects and exposed facets on the thermodynamic stability and photocatalytic characteristics of Ta3N5 for water splitting are studied by applying accurate quantum computations on the basis of density functional theory (DFT) with the range-separated hybrid functional (HSE06). Among the three explored potential candidates for O-enriched bulk Ta3N5 structures with substituted O at N sites and accompanied by interstitial O or Ta-vacancies, the first and third structures are relevant. The four possible (001), (010), (100) and (110) low Miller index exposed facets of Ta(3-x)N(5-y)Oy (y = 7x) are also explored, which show lower formation energies than those of Ta3N5. This highlights O occupation at N sites together with Ta vacancies as native defects in the prepared samples. The most appropriate facets for HER and OER are predicted based on the redox and transport characteristics. Our work predicts (001) and (110) facets only for HER, whereas the (010) facet is predicted for OER. Our findings indicate the importance of understanding the significance of various facets when preparing and testing new material photocatalysts for water splitting reactions.

The effects of native defects and carbon dopant on AlP nanosheet

Developing n- and p-type low dimensional semiconductors is crucial for fabrication high circuit integration density and high speed devices. About how to realize the n- and p-type doping for recently proposed monolayer AlP, we propose the possible schemes. Our investigation shows that aluminum and phosphorus vacancies could render monolayer AlP to be p- and n- type semiconductor. When carbons substitute aluminum or adsorb on phosphorus sites, monolayer AlP is n-type semiconductor. Carbons adsorbed on aluminum sites, the band gap would reduce to 0.98 eV. Carbons substituting phosphorus make monolayer AlP be ferromagnetic semiconductors, and the Curie temperature is estimated to be 403.59 K. Adsorption energies imply carbons chemically adsorb on phosphorus and aluminum sites. Formation energies show carbons substituting phosphorus and phosphorus vacancies can be realized experimentally. Our research provides a useful strategy to tailor monolayer AlP’s properties, even opens up the possibility of applications based on its semiconductors’ properties.

Investigation of 4f-Related Electronic Transitions of Rare-Earth Doped ZnO Luminescent Materials: Insights from First-Principles Calculations.

Rare-earth (RE) doped zinc oxides (ZnO) are regarded as promising materials for application in versatile color-tuned devices. However, the understanding of underlying luminescence mechanism and the rule of 4 f-related electronic transition is still limited, which is full of significance for the exploration of advanced RE-based ZnO phosphors. Thus, a series of ZnO : RE (RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb) phosphors have been investigated by means of first-principles calculations. Meanwhile, we also consider the effect of native defects (VO , VZn ) on the luminescence of ZnO : RE phosphors. Accordingly, four types of electric-dipole allowed transition processes are figured out in ZnO : RE family. Additionally, we manifest that the VO can further improve the luminescent performance of ZnO : RE phosphors, and give insightful guidance to design desired RE-based ZnO materials with excellent luminescence.

Effects of Cd vacancies and unconventional spin dynamics in the Dirac semimetal Cd3As2.

Cd3As2 is a Dirac semimetal that is a 3D analog of graphene. We investigated the local structure and nuclear-spin dynamics in Cd3As2 via 113Cd NMR. The wideline spectrum of the static sample at 295 K is asymmetric and its features are well described by a two-site model with the shielding parameters extracted via Herzfeld-Berger analysis of the magic-angle spinning spectrum. Surprisingly, the 113Cd spin-lattice relaxation time (T1) is extremely long (T1 = 95 s at 295 K), in stark contrast to conductors and the effects of native defects upon semiconductors; but it is similar to that of 13C in graphene (T1 = 110 s). The temperature dependence of 1/T1 revealed a complex bipartite mechanism that included a T2 power-law behavior below 330 K and a thermally activated process above 330 K. In the high-temperature regime, the Arrhenius behavior is consistent with a field-dependent Cd atomic hopping relaxation process. At low temperatures, a T2 behavior consistent with a spin-1/2 Raman-like process provides evidence of a time-dependent spin-rotation magnetic field caused by angular oscillations of internuclear vectors due to lattice vibrations. The observed mechanism does not conform to the conventional two-band model of semimetals, but is instead closer to a mechanism observed in high-Z element ionic solids with large magnetorotation constant [A. J. Vega et al., Phys. Rev. B 74, 214420 (2006)].

Effects of native defects on properties of low temperature grown, non-stoichiomtric gallium nitride

The properties of GaN thin films grown by molecular beam epitaxy at temperatures from 80 to 500 °C under a wide range of Ga:N flux ratios are studied. We found that at growth temperatures as low as ~80 °C, GaN films still have a polycrystalline, columnar morphology with c-axis preferred orientation. Soft x-ray absorption and emission and optical absorption measurements on Ga-rich samples suggest the presence of a partially occupied GaN antisite defect band located at ~1.2 eV below the conduction band minimum. P-type conductivity observed in this LTMBE Ga-rich GaN is consistent with transport within this partially occupied defect band.

Optoelectronic properties and color chemistry of native point defects in Al:ZnO transparent conductive oxide

The effects of native defects (e.g. VO, VZn, H) on the TCO properties and color of an Al:ZnO (AZO) material are investigated using first principles calculations.

Investigation on the effects of native defects on electronic structure in MgB2 by first-principles calculation

The decrease of Currie temperature in milled MgB2 could be caused by some native point defects such as vacancies, antisites, and interstitials. In order to clarify it, the formation energies of the native point defects in MgB2 were examined, and the influence of the stable defects on its electronic structure was investigated by first-principles calculation. It was found that the B interstitials and the B vacancies have the lowest formation energies under Mg-rich (Mg:B>1:2) and Mg-poor (Mg:B>1:2) conditions, respectively, compared to other native point defects. The density of states at the Fermi level for MgB2 with and without point defects is mainly comprised of the B’s p orbital. Under Mg-poor conditions, the partial density of states (at the Fermi level) of the B’s p orbital for MgB2 with B interstitials reduces with the increase of its concentration. Under Mg-rich conditions, the B vacancies first increase and then decrease the partial density of states at the Fermi level of the B’s p orbital as its content increases.

Effects of native defects on the electronic structure and photocatalytic activity in anatase TiO2 by first principles calculations

The crystal structure, electronic structure, optical properties and photocatalytic activity of the native defects in anatase TiO2 were investigated based on the density-functional theory (DFT). The results show that oxygen vacancies (VO) have the lowest formation energy, and thus are easiest to form in the bulk structure. The conduction and valence band moves to the high or low energy region, and the energy gap becomes narrower for the native point defect models. In particular, oxygen interstitials (Oi) have a direct band gap, and new gap states appear in the band gap, which can be responsible for the high photocatalytic efficiency in anatase TiO2. The phenomenon of “impurity compensation” takes place for the oxygen and titanium interstitials. Ti vacancy (VTi) can promote the utilization of solar light by analyzing the absorption spectra. All the calculated results show that Oi and VTi are beneficial in improving the photocatalytic activity of TiO2 in the UV–visible light range.

Analysis of junction properties of gold–zinc oxide nanorods-based Schottky diode by means of frequency dependent electrical characterization on textile

Present work is an effort to reveal the junction properties of gold/zinc oxide (ZnO) nanorods-based Schottky diode by using the frequency dependent electrical properties. The most important electrical parameters such as conductance, resistance, capacitance, and impedance were studied as function of frequency across the series of AC voltages. Moreover, current density–voltage (J–V) was measured to know the performance of present Schottky diode. The effect of native defects was also studied by using cathodoluminescence spectroscopy measured at different accelerating voltage. The textile substrate was used for the growth of ZnO nanorods by using the aqueous chemical growth method and Schottky diode fabrication. Diode fabrication on textile fabric is a step forward toward the fabrication of electronic devices on nonconventional, economical, soft, light weight, flexible, wearable, washable, recyclable, reproducible, and nontoxic substrate.

Effects of Native Defects and Molecular Adsorption On Optical Properties of Two-Dimensional Semiconductors

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Effect of Native Defects on Photocatalytic Properties of ZnO

We have studied the photocatalytic activity of ZnO tetrapods, ZnO powder, and different ZnO nanoparticles. While nanoparticles with small particle size exhibited higher Brunauer–Emmett–Teller (BET)...

Effect of native defects and Co doping on ferromagnetism in HfO2: First‐principles calculations

First-principles calculations of undoped HfO(2) and cobalt-doped HfO(2) have been carried out to study the magnetic properties of the dielectric material. In contrast to previous reports, it was found that the native defects in HfO(2) could not induce strong ferromagnetism. However, the cobalt substituting hafnium is the most stable defect under oxidation condition, and the ferromagnetic (FM) coupling between the cobalt substitutions is favorable in various configurations. We found that the FM coupling is mediated by the threefold-coordinated oxygen atoms in monoclinic HfO(2) and could be further enhanced in electron-rich condition.

A STUDY ON THE MAGNETIC PROPERTIES IN NITROGEN-DOPED ZnO USING FIRST PRINCIPLES

Theoretical calculation based on density function theory (DFT) and generalized gradient approximation (GGA) has been carried out in studying the magnetic properties of nitrogen-doped ZnO . The results show that ferromagnetism (FM) coupling between N atoms is more stable for the majority of 11 geometrically distinct configurations, and N atoms in ZnO have a clear clustering tendency. In addition, the formation and ionization energy of native defects in ZnO is analyzed and discussed. The effect of native defects on FM properties of nitrogen-doped ZnO has also been investigated. It is found that FM state is more favored than the AFM state in the presence of zinc vacancy or oxygen interstitial. In the paper, we also analyze strain effect on FM of nitrogen-doped ZnO .

Magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO: First-principles calculations

The electronic structure and magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO have been investigated using first-principles methods. We show that the magnetic coupling between Gd or Nd ions in the nearest neighbor sites is ferromagnetic. The stability of the ferromagnetic coupling between Gd ions can be enhanced by appropriate electron doping into ZnO:Gd system and the room-temperature ferromagnetism can be achieved. However, for ZnO:Nd system, the ferromagnetism between Nd ions can be enhanced by appropriate holes doping into the sample. The room-temperature ferromagnetism can also be achieved in the n-conducting ZnO:Nd sample. Our calculated results are in good agreement with the conclusions of the recent experiments. The effect of native defects (VZn,VO) on the ferromagnetism is also discussed.