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URE OF INORGANIC COMPOUNDS

Growth and Structural, Optical, and Electrical Properties of Zincite Crystals I. A. Kaurovaa, G. M. Kuz’michevab, and V. B. Rybakovc a

Moscow Open State University, Aleksandrov, 601655 Russia email: [email protected] b Lomonosov State Academy of Fine Chemical Technology, Moscow, 119571 Russia c Moscow State University, Moscow, 119992 Russia Received November 3, 2011

Abstract—An Xray diffraction study of ZnO crystals grown by the hydrothermal method has revealed reflec tions that give grounds to assign them to the sp. gr. P3 rather than to P63mc. The distribution of Zn1, Zn2, O1, and O2 over structural positions, along with vacancies and incorporated zinc atoms, explains the dissym metrization observed in terms of the kinetic (growth) phase transition of the order–disorder type, which is caused by ordering Zn and O atoms over structural positions. The color of crystals of refined compositions (Zn0.975䊐0.025)Zni(0.015)(O0.990䊐0.010) (green) and (Zn0.965䊐0.035)Zni(0.035)O (bright green) is related to differ ent oxygen contents, which is confirmed by the results of electron probe Xray microanalysis and absorption spectroscopy. The degree of the structural quality of crystals, their resistivity, and activation energy are also related to oxygen vacancies. DOI: 10.1134/S1063774513020119

INTRODUCTION Zincite (ZnO, sp. gr. Р6зmс, Z = 2) is a direct and widegap semiconductor (Eg = 3.37 eV); it is charac terized by a high melting temperature (Тm = 1975°С), density (ρ = 5.64 g/cm3), and exciton binding energy (60 meV) [1]. Widegap ZnO crystals are widely used in different fields of piezo, opto, micro, and acoustoelectron ics, in particular, in devices based on bulk and surface acoustic waves (filters, cavities, and delay lines), light emitting devices, and acoustoelectric amplifiers [1–3]. In view of this, the study of their physical properties (in particular, optical and electrical) and establishing the relationship between these properties and struc tural features of crystals and their defects is of particu lar importance. Specifically the latter characterize the material and the possibility of its application. In turn, structural defects depend directly on the crystal growth techniques and conditions of further treat ment. Currently, the main technique for growing large commercial ZnO single crystals is the hydrothermal method, which is based on the crystallization of mate rial from superheated aqueous solutions at elevated temperatures and pressures [4–6]. Hydrothermally grown crystals often contain metal impurities captured from the solution [4], as well as intrinsic point defects, which may affect their physical properties, including color. When alkaline media are used, growth is accom panied by a change in the solution composition and the formation of oxygen vacancies and superstoichio

metric zinc atoms (Zni) at interstitial sites, the coordi nates of which are unknown [5]. In addition, Pb3+, Co2+, Ni+, Fe3+, In3+, Ga3+, Al3+, and Li1+ impurity ions were experiment