| Summary: | 碩士 === 國立中山大學 === 物理學系研究所 === 106 === Dilute magnetic semiconductor by doping of transition ions has been extensively studied, and yet its magnetic origin and electric properties has not been fully understood. Carrier localization and coupling with doping of magnetic cations or any other defects present ferromagnetic behavior. In favor of electrical conductivity, an addition metal is also co-doped in the sample. For example, the aluminum doped CoZnO(CZO) has a much better conductivity for the Al is the trivalent metal and able to contribute one more free electron. It was theorized that the doped Al band hybridizes with the ZnO conduction band to form a degenerate semiconductor. The charge transfer of Al band to the conduction band enhances the electric conduction.
In this study we used the (Co,Al) co-doped ZnO to make the Co0.0476Al0.019Zn0.93O (CAZO) target and grow film at 450°C by RF sputtering with different hydrogen percentage of the working gas to control the oxygen vacancy, and investigate the effects of aluminum doping and vacancies on electron transport.
From the experimental results, it shows that when the growth atmosphere is pure oxygen, the sample is found to be an insulator and the band structure is less affected by defects indicating that the previous theoretical model is not suitable for our samples. As a result,. The Resistance-Temperature measurement confirms that the film has the characteristics of a semiconductor, and the conductivity was improved with the decrease of H2%. The conduction behavior is well described by the combinational model consisted of the thermal excitation and the variable range hopping models. X-ray Diffraction and Transmission Electron Microscopic measurement shows the samples exhibit polycrystalline structure. It was found that not only the thickness of the film changed with the change of H2%, but also the ratio of internal Cobalt to Zinc, indicating that Zinc content was also affected by hydrogen. After confirming which growth conditions have better conductivity characteristics, our future plan is to conduct Hall measurement and superconducting quantum interference device (SQUID) to confirm the carrier concentration of the sample, and whether it has room temperature ferromagnetism.
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