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Abstract
 

To achieve p-type conductivity, Sb doped ZnO has been studied for several decades. But there are still some bottlenecks to obtain stable and reproducible p-type conductivity, which is limiting the widespread use of Sb doped ZnO material. More importantly, the shallow acceptors that donate holes are not determined till now, and it is essential to study what is favorable condition to form the shallow acceptors.

In the present study, Sb-doped ZnO films were fabricated on c-plane sapphire using the pulsed laser deposition method and characterized by the Hall effect measurement, X-ray photoelectron spectroscopy, X-ray diffraction, photoluminescence and positron annihilation spectroscopy.   Systematic studies on the growth conditions with different Sb composition, oxygen pressure and post-growth annealing were conducted.  If the Sb doping concentration is lower than the threshold ~8×10²⁰ cm^-3,the as-grown films grown with appropriate oxygen pressure could be n~4×10²⁰ cm^-3.  The shallow donor was attributed to the Sb_Zn related defect. Annealing these samples lead to the formation of the Sb_Zn-2V_Zn shallow acceptor which subsequently compensated the free carrier.  For samples with Sb concentration exceeding the threshold, the yielded as-grown samples were highly resistive.  X-ray diffraction results showed that the Sb dopant occupied the O site rather than the Zn site as the Sb doping exceeded the threshold, whereas the Sb_Orelated deep acceptor was responsible for the high resistivity of the samples.

Several additionalvibrationmodes, located at 235cm^-1, 511 cm^-1, 534 cm^-1, were observed in the Sb-doped ZnO thin filmsin addition to the host phonons in undoped ZnO sample. The intensity of these additional peaks correlated with the electron concentration/Fermi level. It is plausible that these additional modes are related with the donor defects in Sb doped ZnO samples. 

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