Divacancy-Hydrogen Complexes in Zinc Oxide
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Divacancy-Hydrogen Complexes in Zinc Oxide J. Kuriplach 1, G. Brauer 2, O. Melikhova 1, J. Cizek 1, I. Prochazka 1, and W. Anwand 2 1
Charles University, Faculty of Mathematics and Physics, Department of Low Temperature Physics, CZ-18000 V Holešovičkách 2, Prague, Czech Republic
2
Institut für Strahlenphysik, Forschungszentrum Dresden-Rossendorf, Postfach 510119, D-01314 Dresden, Germany
ABSTRACT In the present work we study Zn+O divacancies filled up with varying amount of hydrogen atoms. Besides the structure and energy-related properties of such defects, we also investigate their capability to trap positrons taking into account positron induced forces. We show that the Zn+O divacancy may trap positrons when up to two hydrogen atoms are located inside the divacancy. The calculated properties are discussed in the context of other computational and experimental studies of ZnO. INTRODUCTION The nature of point defects in zinc oxide is not yet fully understood, but this subject attracts wide attention as it is of vital importance for various technological applications mainly in electronics. An important class of point defects in ZnO is represented by hydrogen-related defects that are also often considered in relation to the n-type conductivity of ZnO materials [1,2]. Recently, it has been found that nominally undoped commercially available ZnO single crystals contain an appreciable amount of hydrogen at a level of at least 0.3 at.% [3]. The forms in which such hydrogen atoms are incorporated into the ZnO lattice are not precisely known at present, and there are several possibilities, in principle. In particular, hydrogen may occupy interstitial positions and/or may be present in the form of H2 molecules in ‘channels’ along the caxis of the hexagonal ZnO lattice [1]. Hydrogen may also form complexes with other impurities though their concentrations are usually much smaller than that of H, as found in [3]. Furthermore, hydrogen atoms can enter open volume defects, like oxygen and zinc vacancies (see e.g. [4]) and related defects. Positron annihilation techniques are sensitive to such kind of defects and, as shown in [3], positron trapping in hydrothermally-grown ZnO materials occurs in Zn-vacancy-hydrogen related complexes. Namely, a suggestion has been given that positrons may get trapped in a Zn-vacancy occupied by one hydrogen atom. In the present work, we extend our study to Zn+O divacancies containing hydrogen atoms (VZn+O+nH complexes). We investigate their structure, energy-related properties, and also positron characteristics taking into account positron induced forces acting on the ions surrounding studied defects. Our previous positron studies as well as further motivations, explanations and references to other related literature can be found in refs. [3,5].
COMPUTATIONAL METHODS Realistic configurations of studied defects were obtained by means of relaxing the total energy of corresponding supercells with respect to atomic positions. In particular, the Vienna ab initio simulation package (V
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