First-principles study of the structure and stability of oxygen defects in zinc oxide (original) (raw)
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Interaction of zinc interstitial with oxygen vacancy in zinc oxide: An origin of n-type doping
Solid State Communications, 2012
Interaction of a zinc interstitial (Zn i) with an oxygen vacancy (V O) was investigated to understand an origin of natively n-type characteristics of ZnO using density functional theory with the hybrid functional. The V O-Zn i complex is formed with a formation of 3.82 eV and is a shallow donor with þ 1 charge state near the conduction band minimum. Its formation energy, however, is not low enough to be stable thermodynamically. Energy barrier for Zn i migration in the V O-Zn i complex is studied to consider its existence from kinetic aspect, and a high value of 1.3 eV is obtained with the kick-out process. Therefore, the bound Zn i to V O can exist and supply electrons for native n-type ZnO kinetically.
Physical Review B, 2006
Density-functional theory ͑DFT͒ calculations of intrinsic point defect properties in zinc oxide were performed in order to remedy the influence of finite-size effects and the improper description of the band structure. The generalized gradient approximation ͑GGA͒ with empirical self-interaction corrections ͑GGA+ U͒ was applied to correct for the overestimation of covalency intrinsic to GGA-DFT calculations. Elastic as well as electrostatic image interactions were accounted for by application of extensive finite-size scaling and compensating charge corrections. Size-corrected formation enthalpies and volumes as well as their charge state dependence have been deduced. Our results partly confirm earlier calculations but reveal a larger number of transition levels: ͑1͒ For both the zinc interstitial as well as the oxygen vacancy, transition levels are close to the conduction band minimum. ͑2͒ The zinc vacancy shows a transition rather close to the valence band maximum and another one near the middle of the calculated band gap. ͑3͒ For the oxygen interstitials, transition levels occur both near the valence band maximum and the conduction band minimum.
In this paper, all electron full-potential linearized augmented plane wave plus local orbitals method has been used to investigate the structural and electronic properties of polar (0001) and non-polar (10ī0) surfaces of ZnO in terms of the defect formation energy (DFE), charge density, and electronic band structure with the supercell-slab (SS) models. Our calculations support the size-dependent structural phase transformation of wurzite lattice to graphite-like structure which is a result of the termination of hexagonal ZnO at the (0001) basal plane, when the stacking of ZnO primitive cell along the hexagonal principle c-axis is less than 16 atomic layers of Zn and O atoms. This structural phase transformation has been studied in terms of Coulomb energy, nature of the bond, energy due to macroscopic electric field in the [0001] direction, and the surface to volume ratio for the smaller SS. We show that the size-dependent phase transformation is completely absent for surfaces with a non-basal plane termination, and the resulting structure is less stable. Similarly, elimination of this size-dependent graphite-like structural phase transformation also occurs on the creation of O-vacancy which is investigated in terms of Coulomb attraction at the surface. Furthermore, the DFE at the (10ī0)/(ī010) and (0001)/(000ī) surfaces is correlated with the slab-like structures elongation in the hexagonal a- and c-axis. Electronic structure of the neutral O-vacancy at the (0001)/(000ī) surfaces has been calculated and the effect of charge transfer between the two sides of the polar surfaces (0001)/(000ī) on the mixing of conduction band through the 4s orbitals of the surface Zn atoms is elaborated. An insulating band structure profile for the non-polar (10ī0)/(ī010) surfaces and for the smaller polar (0001)/(000ī) SS without O-vacancy is also discussed. The results in this paper will be useful for the tuning of the structural and electronic properties of the (0001) and (10ī0) ZnO nanosheets by varying their size.
Defect energetics in ZnO: A hybrid Hartree-Fock density functional study
Physical Review B, 2008
First-principles calculations based on hybrid Hartree-Fock density functionals provide a clear picture of the defect energetics and electronic structure in ZnO. Among the donorlike defects, the oxygen vacancy and hydrogen impurity, which are deep and shallow donors, respectively, are likely to form with a substantial concentration in n-type ZnO. The zinc interstitial and zinc antisite, which are both shallow donors, are energetically much less favorable. A strong preference for the oxygen vacancy and hydrogen impurity over the acceptorlike zinc vacancy is found under oxygen-poor conditions, suggesting that the oxygen vacancy contributes to nonstoichiometry and that hydrogen acts as a donor, both of which are without significant compensation by the zinc vacancy. The present results show consistency with the relevant experimental observations.
$\ textit {Ab-initio} $ many-body calculations of the oxygen vacancy in ZnO
We have applied the many-body ab-initio diffusion quantum monte carlo (DMC) method to calculate the band gap of ZnO and to study the oxygen vacancy in this material. DMC calculations clearly rule out the oxygen vacancy as the source of the persistent n-type conductivity in ZnO. The DMC results were compared with Hartree-Fock, the Heyd-Scuseria-Ernzefhof (HSE) hybrid functional and other approximations of density functional theory (DFT). DMC predicts the band gap at 3.43(9) eV. DMC and HSE show that the thermodynamic transition levels of the oxygen vacancy are deep, between 1.8 and 2.5 eV from the valence-band maximum. The oxygen vacancy is unlikely to be the source of the persistent n-type conductivity in ZnO, confirming previous DFT calculations. Despite this agreement between DMC and HSE, we found two major differences: (i) the oxygen vacancy formation energy is about 1 eV higher in DMC than in HSE and other DFT approximations and (ii) DMC predicts a positive U behavior for the oxygen vacancy while HSE and other DFT approximations predict the opposite. These results are discussed in conjunction with recent experiments.
New insights into the role of native point defects in ZnO
Journal of crystal growth, 2006
Using first-principles methods based on density functional theory and pseudopotentials, we have performed a detailed study of native point defects in ZnO. Contrary to the conventional wisdom, we find that native point defects are unlikely to be the cause of the frequently observed unintentional n-type conductivity. Oxygen vacancies, which have most often been invoked as shallow donors, have high formation energies in n-type ZnO, and are actually deep donors with a very high ionization energy. Zinc interstitials are shallow donors, but have high formation energies in n-type ZnO; in addition, they are fast diffusers, and thus unlikely to be stable in n-type ZnO. Zn antisites are also shallow donors, and have even higher formation energies than zinc interstitials. They may play a role under non-equilibrium conditions such as in irradiation experiments. Zinc vacancies are deep acceptors and may act as compensating centers in n-type ZnO. Oxygen interstitials are stable in the form of electrically inactive split interstitials as well as deep acceptors at the octahedral interstitial site under n-type conditions. Our results may provide a guide to more in-depth experimental studies of point defects in ZnO and their influence on the control of doping.
Ab-initio study of charged oxygen defects in Zn2P2O7
Nucleation and Atmospheric Aerosols, 2019
First principles calculations using projector augmented wave potentials and generalized gradient approximations predicts the structural relaxations due to neutral and positively charged oxygen defects (+1 and +2) in bulk Zn2P2O7 leads to asymmetric distortion around the vacancy site. Electronic Density of states (DOS) analysis shows presence of defects states mainly contributed by Zn s, P p and O p states near the conduction band minimum for the single and double positively charged oxygen vacancies which are lower vacancy formation energy compared to neutral vacancy.
2014
ZnO nanoparticles, synthesized adopting a facile chemical precipitation route, are studied here. The structural, optical and electronic properties of prepared ZnO nanoparticles were extensively investigated employing X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive analysis by X-rays (EDAX), X-ray photoelectron spectroscopy (XPS), UV-vis absorption and fluorescence (FL) spectroscopy. The XRD analysis revealed hexagonal wurtzite phase 26.1-29.6 nm size ZnO nanocrystallites. This observation gets further support from TEM images where particles of 25-30 nm size are vividly seen. Interestingly, oxygen rich stoichiometry of nanoparticles is detected via zinc and oxygen emission lines of EDAX spectrum. XPS analysis establishes coexistence of lattice oxygen (O L ), interstitial oxygen (O i ) and oxygen vacancy (V O ) in ZnO nanoparticles. In line with EDAX analysis, XPS investigations substantiate interstitial oxygen rich composition of nanoparticles. Blue shift of absorption energy, as observed in the UV-vis spectrum of ZnO nanoparticles, typically manifests quantum confinement effect. Such transitions indicate the occurrence of various discrete energy states of prepared nanoparticles. FL spectroscopic investigations ascertain the existence of these discrete states by probing the radiative transitions arising among such states. Finally, FL study not only demonstrates visible emissions emanating from the oxygen defect states but more remarkably, in concurrence with EDAX and XPS analysis, establishes the excess of interstitial oxygen defects in prepared ZnO nanoparticles.
Many-body GW calculation of the oxygen vacancy in ZnO
Physical Review B, 2010
Density functional theory (DFT) calculations of defect levels in semiconductors based on approximate functionals are subject to considerable uncertainties, in particular due to inaccurate band gap energies. Testing previous correction methods by many-body GW calculations for the O vacancy in ZnO, we find that: (i) The GW quasi-particle shifts of the V O defect states increase the spitting between occupied and unoccupied states due to self-interaction correction, and do not reflect the conduction versus valence band character. (ii) The GW quasi-particle energies of charged defect states require important corrections for supercell finite size effects. (iii) The GW results are robust with respect to the choice of the underlying DFT or hybrid-DFT functional, and the (2+/0) donor transition lies below midgap, close to our previous prediction employing rigid band edge shifts.
JOURNAL DE PHYSIQUE The calculated defect structure of ZnO
Chemistry Department, ~n i v e r i i t~ of Manchester, Manchester, MI3 9PL, England RBsumk. -Les energies des dCfauts fondamentaux dans ZnO sont calculees et comparCes avec les resultats experimentaux obtenus par Kroger. L'Cnergie correspondante a la bande de conduction est calculCe en considerant des defauts neutres ou charges. Les effets de dopage avec des impuretes cationiques : Li+, N a + , A13+, ~a~+ , In3+ et H + sont analyses. Enfin les energies associees aux centres F f et F sont calculkes theoriquement.