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Ab INITIO CALCULATIONS OF HYDROGEN IMPURITES IN ZnO A. Useinov 1, A. Sorokin 2, Y.F. Zhukovskii 2, E. A. Kotomin 2, F. Abuova 1, A.T. Akilbekov 1, J. Purans 2 L. N. Gumilyov Eurasian National University, 3 Munaitpasova, Astana, Kazakhstan Institute of Solid State Physics, 8 Kengaraga str., University of Latvia, Riga Details of calculation method Zinc oxide modified by varios metallic dopants can be used as suitable low-cost substitute for indium-tin oxide when manufacturing the solar batteries and optoelectronic devices [1]. Therefore, the atomic and electronic structure of defective ZnO continues to attract great attension due to a number of promising technological applications. In this study, we present analyze the influence of neutral H impurity defects on the redistribution of the electronic charge, the band structure and energy of defect in the ZnO bulk. Special attention is paid to an interstitial hydrogen atom (H i ) [3]. Interstitial and substitutional H have been shown by first-principles calculations to be shallow donors, which contribute to the n-type conductivity in ZnO. When ZnO is doped by H, its electrical conductivity increases simultaneously with retain of high optical transparency. Introduction large-scale ab initio DFT calculations have been performed using the formalism of linear combination of localized atomic functions (LCAO) including optimized atomic basis sets combined PBE0 hybrid exchange-correlation functional, as implemented into CRYSTAL09 code [2]. For periodic system, The reciprocal space integration was performed by sampling the Brillouin zone with an 2 × 2 × 1 Pack-Monkhorst mesh. To achieve high accuracy, large enough tolerances of 7, 7, 7, 7, and 14 were chosen for the Coulomb overlap, Coulomb penetration, exchange overlap, first exchange pseudo- overlap, and second exchange pseudo-overlap, respectively. Interstitial H in ZnO bulk Fig. 2. Density of states (DOS) of a perfect (a) and the one H impurity (b) in ZnO 3 ×3 ×2 supercell Conclusions Hybrid exchange-correlation functionals provide much better correlation of calculated band structures with experiment, including width of band gap and position of defect levels. Our calculations showed that hydrogen creates a H-O with O atom and leads to the delocalization of electronic charge on the nearest atoms. As in earlier studies, we confirm that the impurity hydrogen H i give rise to shallow levels, close to the conduction band minimum of ZnO, which can explain the increase of the electrical conductivity. References 1. D.C. Reinolds, D.C. Look, B. Jogai, C.W. Litton, G. Gantwell, W.C. Harsch, Phys. Rev. B 60, 2340 (1999). 2. R. Dovesi, V.R. Saunders, C. Roetti, et al. CRYSTAL-2009 User’s Manual (University of Torino, 2009). 3. Mao-Hua Du and Koushik Biswas, Phys. Rev. Letters, PRL 106, 115502 (2011) 4. Federico Gallino, Gianfranco Pacchioni, and Cristiana Di Valentin, J. Chem. Phys., 133, 144512 (2010) To estimate electronic properties of interstitial hydrogen atom, we optimize position of H i per 3×3×2 supercell with frozen geometry of lattice. We have constricted the electronic charge redistribution (see Fig.3) under influence of H impurity and density of states (see Fig.2). In this study the ZnO bulk described with periodic 3 × 3 × 2 supercell models (see Fig.1). The lattice parameters of supercell a = 3.28 and c = 5.18 Å. The H dopants concentration 1.4%. Fig. 1. Arrangement of the interstitial hydrogen atom H i in the 3×3×2 supercell of ZnO Fig. 3 The total and difference electronic density distributions for H impurity. Bond length between the oxygen atom and hydrogen is 1.561 Å. The shift of the hydrogen atom in the bulk ZnO is x = 0.09052 Å in the opposite direction of the nearby oxygen atom. For calculate of defect formation energy we have consider follow expression: Where – defect formation energy, – total energy of defective structure, – energy of a perfect crystal and – energy of isolated H atom. The calculated formation energy of defect is found to be 1.13 eV. To describe the electron density redistribution we have been constricted a difference charge density maps projected on characteristic plane of defect as shown in Fig. 3 a b Redistribution of the electronic density to describe of ground impurity H atom clearly shows some transfer of charge toward the channel inside ZnO lattice which contributes to the n – type conductivity in accordance with earlier performed theoretical study [4], thus electrical conductivity increase. This study was supported by ERAF project Nr. 2010/0272/2DP/2.1.1.1.0/10/APIA/VIAA/088

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Lattice defects in oxides.

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