The effects of postdeposition annealing conditions on structure and created defects in Zn 0.90 Co 0.10 O thin films depo
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_ Faculty of Engineering and Natural Sciences, Sabancı University, Tuzla 34956, Istanbul, Turkey; and _ Nanotechnology Research and Application Center (SUNUM), Sabancı University, Tuzla 34956, Istanbul, Turkey
Tezer Fırat Department of Physics Engineering, Hacettepe University, 06800 Beytepe, Ankara, Turkey
S.Ismat Shah Department of Material Science and Engineering, Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716
Feray Bakan and Ahmet Oral
_ Faculty of Engineering and Natural Sciences, Sabancı University, Tuzla 34956, Istanbul, Turkey; and _ Nanotechnology Research and Application Center (SUNUM), Sabancı University, Tuzla 34956, Istanbul, Turkey (Received 31 July 2012; accepted 3 December 2012)
We analyze the effect of postdeposition annealing conditions on both the structure and the created defects in Zn0.90Co0.10O thin films, which deposited on the Si(100) substrates by the radio frequency magnetron sputtering technique using a homemade target. The dependence of the number and distribution of defects in homogeneously substituted Co12 for Zn12 ions in ZnO lattice on the annealing conditions is investigated. Orientations of thin films are in the [0002] direction with a surface roughness changing from 67 6 2 nm to 25.8 6 0.6 nm by annealing. The Co12 ion substitution, changing from 7.5% 6 0.3% to 8.8 6 0.3%, leads to the formation of Zn–O–Co bonds instead of Zn–O–Zn bonds and splitting of the Co 2p energy level to Co 2p1/2 and Co 2p3/2 with an energy difference of 15.67 6 0.06 eV. The defects in the lattice are revealed from the correlations between Zn–O–Co bonds and intensity of the Raman peak at around 691 cm 1. In addition, the asymmetry changes of O 1s peak positions in the x-ray photoelectron spectra are in agreement with the Raman results. I. INTRODUCTION
ZnO is one of the most widely investigated oxide semiconductors because of the room temperature magnetic applications.1–3 Numerous theoretical and experimental studies have been performed on transition metal-doped ZnO to understand the mechanisms of ferromagnetism.4–13 Nevertheless, the origin of magnetic behavior of transition metal-doped ZnO structure4–13 is still not well understood. There are three main suggestions for the magnetic behavior in doped ZnO. The first one is the p–d hybridization of orbitals due to holes in the lattice.5,6 The second one is the s–d hybridization in the n-type semiconductor,7 and the third potential mechanism is the formation of transition metal clusters6,8,10,14 or the secondary phases in the ZnO lattice.14,15 These results have actually increased the debate on the magnetic properties of ZnO, rather than giving a definite answer. Nowadays, another suggestion is focused on the shallow donor/acceptor levels originating from defects in the ZnO crystal.16,17 Recent findings have shown the importance of defects, in addition to transition atoms in lattice, on the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.422 708
J. Mater. Res., Vol. 28, N
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