Abstract
By using positron annihilation spectroscopy methods, we have experimentally demonstrated the creation of isolated zinc vacancy concentrations >1020 cm−3 in chemical vapor transport (CVT)-grown ZnO bulk single crystals. X-ray diffraction ω-rocking curve (XRC) shows the good quality of ZnO single crystal with (110) orientation. The depth analysis of Auger electron spectroscopy indicates the atomic concentrations of Zn and O are almost stoichiometric and constant throughout the measurement. Boltzmann statistics are applied to calculate the zinc vacancy formation energies (Ef) of ~1.3–1.52 eV in the sub-surface micron region. We have also applied Fick’s 2nd law to calculate the zinc diffusion coefficient to be ~1.07 × 10−14 cm2/s at 1100 °C. The zinc vacancies began annealing out at 300 °C and, by heating in the air, were completely annealed out at 700 °C.
Highlights
In this letter, we present results on the formation energy and diffusivity of zinc vacancies in ZnO, where a large number of zinc vacancies (1017 < VZn ~ 1020) are created in thermodynamic equilibrium by oxygen annealing
Chemical vapor-transport-grown ZnO crystals were placed in Heraeus high-purity quartz ampoules that were evacuated using roughing and turbo molecular pumps and that were baked at ~150 °C overnight to remove residual water vapor
Depth-resolved positron annihilation spectroscopy (PAS) Doppler broadening measurements were performed at the Washington State University (WSU)
Summary
By using positron annihilation spectroscopy methods, we have experimentally demonstrated the creation of isolated zinc vacancy concentrations >1020 cm−3 in chemical vapor transport (CVT)-grown ZnO bulk single crystals. The most prevalent way of creating zinc vacancies has been either by electron or laser irradiation[4,5], i.e., by non-equilibrium thermodynamic processes that lead to the simultaneous creation of compensating defects such as zinc interstitials, oxygen interstitials, and oxygen vacancies. The creation of such defects is relatively hard to avoid and control. A study of the formation energy and diffusion coefficient that is more reliable relative to an approach where zinc vacancies are created by a non-thermodynamic-equilibrium process such as, an electron irradiation or bombardment using a laser exposure
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