單一摻鈷氧化鋅奈米柱之電子傳輸行為研究

Abstract

在本篇論文利用「介電泳動法」將不同濃度的單根摻鈷氧化鋅奈米柱跨接在電極上，並且結合電子束微影技術及聚焦離子束顯微鏡技術製作出單根的電性量測元件，得知在不同摻雜比例的單一摻鈷氧化鋅奈柱之完整電學性質。 從兩點式的電性量測結果可以發現，隨著鈷之參雜濃度提升， 奈米柱磁性與電阻也隨之上升，且可以用BMP模型獲得一個合理的解釋， 接著為了瞭解此種接觸方法對真實電阻之影響，儘可能避除掉接觸電阻的影響，於是製作出四點式的電性量測元件，利用三種不同的電性量測與計算方式得知單根摻鈷氧化鋅電阻率，由結果得知可製作出良好電極，接觸電阻近乎可忽略。 接下來為了得之奈米柱之活化能和其在低溫下的電子傳輸行為， 對元件進行變溫電性量測，在高溫下，電子的行為將由熱活化傳輸所主導，且求得奈米柱之活化能約為33.67~27.26meV， 且發現在升溫通電流的情形下奈米柱會因為無法承受太高的電流而燒毀或部分結構損毀， 隨著溫度下降，電子處在高雜質環境下，容易被許多雜質所束縛住，而改利用Hopping的機制進行電子傳導， 由電阻率跟溫度的關係可得知在低溫中並無變程跳躍的導電機制出現，而是由文獻得知是因在低溫中因環境熱能不足而只傳導到D-band所造成。 最後，發現氧化鋅奈米柱放置在空氣中經過長時間會造成電阻率升高，其原因來自於奈米柱表面之氧吸附，將原件置入真空中有助於氧之脫附造成電阻率之下降， 未來可將奈米柱之表面進行一些修飾，使得奈米柱獲得穩定且長久的電性。

In this thesis, by using e-beam lithography, dielectrophoresis and focused ion beam techniques, we demonstrate methods to manipulate, align and make electrical contacts with a single Co:ZnO nanorod on metal pads. With this technique, we can measure the entire electric properties for ZnO nanrods doped with various ratio of cobalt. To eliminate the influence of contact resistance and to accurately determine the resistivity of a single nanorod, we devised a four-point-probe contact device. The electrical measurements were analyzed with three different measuring methods to determine the resistivity of the single Co:ZnO nanorod. In order to investigate the activity energy and electron transport properties at low temperatures, temperature dependent resistivity measurements were carried out room temperature to 80K. At high temperature, the electrron transport properties are dominated by thermally activated mechanism. The activity energy is determined to be 33.67~27.26meV. At low temperature, electrons are localized by the impurities and the nearest-neighbor hopping mechanism dominates the carrier transport at low temperature. When the ZnO nanorods were exposed under air for long time, the resistivity of ZnO nanorods was found to increase due to the oxygen absorption on surface.