Excess Zn in ZnO was experimentally investigated. The ZnO samples tested were prepared by heat treatment of ZnO powder or polycrystalline ceramics at a temperature of 900 °C and at fixed Zn pressures from 0.2 to 0.6 of saturated Zn vapour pressure at a given temperature. To determine the excess Zn, atomic absorption photometry of Zn vapour was used under conditions of solid-vapour equilibrium. The optical absorbance, proportional to the concentration of Zn atoms in the vapour phase, was registered photoelectrically on the Zn resonance line. During the atomic absorption photometry measurements all excess Zn was extracted from the solid state into the vapour phase. The analysis of the temperature dependence of Zn pressure indicated that the value of Zn excess lies in the concentration interval of 10 18 -10 19 cmand depends on the sample history and the conditions of preliminary heat treatment. The experimental results were used for preliminary estimation of high-temperature defect equilibrium in ZnO. Chemical analysis is not a reliable technique for evaluating the excess Zn in ZnO. Chemical analysis can only serve as a qualitative technique for comparing different samples. In our investigations of atomic absorption photometry of polycrystalline II-VI materials it became evident that the metal component adsorbed on crystallite surfaces must be taken into account [5]. In Ref.[6] different HTDE models from different authors are compared. ZnO exhibits n-type high-level electrical conductivity, which is due to intrinsic donor [7] or to hydrogen as a shallow donor [8]. The dominating high-temperature defects are interstitial Zn [9][10][11] or oxygen vacancies [2,12]. Atomic absorption photometry studies of the nonstoichiometry of II-VI compounds have shown that the analytically determined concentration of the metal component excess appears to be bigger than the concentration of electrically active defects [13,
PACS 61.50. Nw, 61.72.Ji, 64.70.Hz Zn excess in ZnO is built up automatically at high temperatures. Excess Zn in hydrothermally grown ZnO single crystals were investigated by the atomic absorption photometry (AAP) method. To determine the excess zinc in ZnO samples, the AAP of zinc vapour was used in the conditions of solid-vapour equilibrium. Zn AAP allowes to eliminate excess Zn connected differentially in ZnO samples. To fix Zn non-stoichiometry, all the ZnO samples tested were previously heat treated at temperature interval from 850 to 900 0 C and at fixed Zn vapour pressures from 0.1 to 0.9 of saturated zinc vapour pressure at given treatment temperature. The analysis of temperature dependence of zinc vapour pressure indicated that the impurity metals take active role in the determination of non-stoichiometric zinc. The impurities Mn, Fe, Co, Ni and Cu form oxides which will reduce during annealing in Zn vapor up to metals form. During AAP measurement in optical cuvette, these metals react with ZnO and give additional Zn vapor pressure.1 Overview ZnO is used in a wide range of scientific and technological applications, such as optoelectronic devices, varistors, devices for surface acoustic waves and planar optical waveguides, transparent electrodes and transparent windows for a solar cell, gas sensors, flat panel diplays, catalysts, ferroelectric memories and spintronic devices, antibacterial agent and ZnO can satisfy the commercial desire for blue and ultraviolet light emitting devices -it is suitable to grow the high quality ZnO homoepilayer on the ZnO substrate [1][2][3]. For that reason, it is important to produce high quality ZnO bulk crystals for substrates of ZnO-related devices. The hydrothermal method has an advantage to grow large bulk crystals due to the growth under low supersaturation [4][5][6]. Some doubts were raised about the quality of such crystals because they have often exhibited large X-ray rocking curve widths and low photoluminescence yield with large linewidths [7]. But if the surface damage due to mechanical polishing was overcome, hydrothermal ZnO crystals provided a competitive substrate for homoepitaxial growth [7,8]. As the hydrothermal crystals invitably involve alkali metals from solution and small amounts of metallic impurities then one of the problems in hydrothermally grown ZnO crystals is the contamination of the crystal with metallic impurities. The concentration of impurities exceeds often the concentration of intrinsic defects. The colourless crystals were found with a total impurity content of less than 1 ppm [4,9] but it is found that the green colouration of the hyrothermally grown crystals may be due to the presence of iron in concentration up to 60 ppm [9]. The solubilities of metal oxides in ZnO are high. For example the solubility of Fe in ZnO is 7 mole% at 800 0 C [10]. Fe in ZnO appears as a result of the corrosion of the inner wall of the autoclave [11]. The thermal treatment of ZnO crystal results in the formation of associates between metal impurities [12,...
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