ZnO 1-x Te x thin films deposited by reactive magnetron co-sputtering: composition, structure and optical properties
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ZnO1-xTex thin films deposited by reactive magnetron co-sputtering: composition, structure and optical properties O. Sánchez1, A. Climent2, M. Fernández Barcia1, 2,*, O. Martínez Sacristán 3, and M. HernándezVélez2 1 Instituto de Ciencia de Materiales de Madrid (CSIC). Sor Juana Inés de la Cruz, 3, 28049 Madrid. Spain 2 Dpto. Física Aplicada Universidad. Autónoma de Madrid, Cantoblanco 28049 Madrid. Spain 3 UGdS-Optronlab Group, Universidad de Valladolid, Pº de Belén 11, 47011-Valladolid, Spain * currently at Institute for Complex Materials, IFW Dresden, Helmholtzstr. 20, 01069 Dresden. Germany ABSTRACT ZnO1-xTex thin films were deposited by DC reactive magnetron co-sputtering using pure Zn and Te targets. Te atomic concentration in the films ranged from x=0 to 0.33 by adjusting the applied power on the targets or varying the cathode-substrate distance. Chemical composition and crystalline structure were determined by RBS experiments and X-ray Diffraction, respectively. For low Te atomic concentrations (x≤0.04) the deposited ZnO1-xTex films showed a crystalline structure ZnO wurtzite type however, for increasing Te concentration significant broadening and decreasing intensities of the main peaks belonging to pure ZnO films together with some weak peaks characteristic of crystalline Trizinc Tellurate salt have appeared. For the highest x values some non-identified weak peaks beside to some others peaks corresponding to the crystalline phases mentioned above as well as, a broad band probably associated to amorphous TeO2 phase were observed. A preliminary optical characterization of the samples point out the possibility of different electronic transitions within the ZnO band gap. INTRODUCTION The scientific and technical research about II-VI semi-conductor and their derivatives keep a lot of attention and research effort as very versatile materials for different industrial applications. In recent years, ZnO1-xTex thin films have revealed very interesting applications in solar energy conversion technology both as a transparent conductor oxide (TCO) for photovoltaic (PV) and for multiband, single junction and high-efficiency photovoltaic devices. On one hand, Zinc Oxide (ZnO) stands out because its attractive properties such as a wide direct gap of 3.37 eV at RT and large exciton binding energy (60 meV), with direct applications in solar cells fabrication and different optoelectronic devices, in addition to the possibility to be used as transparent semiconductor windows. ZnO can be easily doped with metals and there exist many reports in which Al, Ga and In doped ZnO films [1, 2] increasing its possible applications in solar cells field. Growth of ZnO films by different methods gives place to a nonintentioned n type doping. This fact is mainly due to the appearance of oxygen vacancies (Vo) that lead to imbalanced stoichiometric in the compound. One way of balance out these vacancies is by doping with isoelectronic impurities that may take up the oxygen vacancies. A recommendable element to obtain this result is Tellurium
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