The Effect of Mn Incorporation on the Structural, Morphological, Optical, and Electrical Features of Nanocrystalline ZnO
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studies have recently been focused on transparent conductive oxide (TCO) application. High electrical conductivity, optical transmission, and better stability are among the most important features of the TCO films. Generally, tin-doped indium oxide (ITO) has been used as a TCO for many implementations because of its excellent characteristic properties. However, ITO has some disadvantages such as high toxicity, high cost, and scarcity.[1] Thus, researchers have made effort to develop alternative materials for ITO. Zinc oxide (ZnO) is one of them because of its band gap of 3.37 eV at room temperature (RT), the large exciton binding energy of about 60 meV, and distinguished surface effect (with up to 1.53-eV band-bending)[2–4]; it has attracted intensive research efforts for its versatile applications such as memory,[5] transistors,[6] light emission,[7] and gas sensing.[8] Besides, ZnO is one of the most important degenerate semiconductors. The
MEHMET YILMAZ, Assistant Professor, is with the Advanced Materials Research Laboratory, Department of Nanoscience and Nanoengineering, Graduate School of Natural and Applied Sciences, University of Atatu¨rk, 25240 Erzurum, Turkey, and also with the Department of Elementary Science, K.K. Education Faculty, University of Atatu¨rk, 25240 Erzurum, Turkey. Contact e-mails: [email protected]; [email protected] S ¸ AKIR AYDOG˘AN, Full Professor, Assistant Dean, is with the Department of Physics, Faculty of Science, University of Atatu¨rk, 25240 Erzurum, Turkey. Manuscript submitted August 26, 2014. Article published online April 2, 2015 2726—VOLUME 46A, JUNE 2015
Fermi level position of un-doped ZnO film is approximately 2.8 eV high on the valence band maximum. With sufficient doping, it will show low sheet resistance. Non-intentionally doped ZnO films are conductive due to the deviations from stoichiometry. Zinc interstitial and oxygen vacancy are generally considered as intrinsic shallow donors that cause n-type conductivity.[9] Namely, the Fermi level in un-doped ZnO is close to the conduction band, indicating the non-intentionally doped ZnO is a n-type semiconductor. Furthermore, the conductivity of un-doped ZnO film is not enough, especially for transparent conducting oxides applications. Extrinsic doping atoms may improve the conductivity of the film. ZnO can easily be n-type, while the ptype is difficult. The dopant atoms are built into the Zn lattice sites, providing additional electrons. It is known that the carrier density increases with the doping. Heavily doped ZnO film behaves like a metal instead of semiconductor. Many studies have focused on Mndoped ZnO in bulk or thin-film form, keeping different views. For example, Shinde et al.[10] have studied on characteristic properties of Mn-doped ZnO thin films via spray pyrolysis technique. Zhang et al.[11] have observed a single UV emission at 3.25 eV belonging to nanocrystalline ZnO:Mn thin films passivated by Mn. Additionally, some researchers have been search out that Mndoped ZnO has a DMS properties.[12,13] At the same ti
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