Structural Properties and Doping of Zn 1-x (Mg,Li) x OMaterials
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Structural Properties and Doping of Zn1-x(Mg,Li)xO Materials R. E. Melgarejo, M.S. Tomar∗, A. Hidalgo, R. S. Katiyar1 Physics Department, University of Puerto Rico, Mayagüez, PR 00681, 1 Physics Department, University of Puerto Rico, Rio Piedras, PR 00931 ABSTRACT The possibility of the solid solutions with MgO provides the opportunity in ZnO/ZnMgO quantum well structures. The recent observation that n-type conductivity in ZnO is due to hydrogen doping open the avenue for p-doping to form p-n junction devices in ZnO.. We report on the synthesis and structural properties of Zn (Mg,Li)O. The possibility of p-doping by P has been explored.
INTRODUCTION Al doped ZnO thin films increase the conductivity without sacrificing its optical properties [1]. Theoretical prediction and the recent observation [2,3] that the n type conductivity in ZnO is due to hydrogen incorporation, has attracted a lot of attention for the p doping. Zinc oxide films have been used as transparent conductors, surface acoustic wave (SAW) devices and oxygen sensors [4]. We demonstrated that Zn1-xMgxO makes a solid solution [5] for ~ 12 at % MgO without changing the wurtzite structure of ZnO. It provides the opportunity of band gap engineering for optoelectronic devices. Also, the observed small ferroelectric response [7] in Zn1-xLixO was proposed to be due to the structural modification due to off-centered dopants Li+ (0.60Å) on host Zn2+ (0.73 Å) in wurtzite structure. Thus, an understanding of the bonding character in Zn1-x(LiyMg1-y)xO material is important for the development p-n junction based blue emission devices. We investigate here the structural properties of Zn1-x(LiyMg1-y)xO prepared by solution chemistry synthesis route. EXPERIMENTAL DETAILS For the synthesis of Zn1-x(LiyMg1-y)xO, precursors were simple salts such as, acetates of zinc, magnesium, and lithium with methoxy ethanol and 2-ethylhexanoic acid as solvents. Stoichiometric ratios of the desired compositions were dissolved in methoxy ethanol and 2ethylhexanoic acid. The solutions of the individual salts and solvents were mixed hot. This solution was then refluxed to form a clear solution. Part of the solution was dried on a hot plate with constant stirring to make the powder. The powder was ground in agate crucible, and annealed at different temperatures to study the evolution of chemical reaction. Another part of the solution was heated to make a denser solution for spin coating. Thin films were deposited on Pt (Pt/TiO2/SiO2/Si) substrate by spin coating (Headway spinner) at 3500 rpm. The materials were characterized using x-ray diffraction and Raman spectroscopy.
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Material Characterization The Raman measurements were performed using an ISA T64000 triple monochromator with 1800 grooves/mm gratings. An optical microscope with 80X objective was used to focus the excitation radiation, a 514.5 nm line from a Coherent Innova 99 Ar+ laser, as well as to collect the backscattered radiation. Room temperature Raman spectra of the Zn1-xLixO for
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