原位製備並五苯平面有機自旋電子傳輸元件之電性及磁性傳輸特性研究

Abstract

有機半導體的自旋電子注入與傳輸是一個尚在發展的研究課題,自旋電子在有 機材料內的傳輸機制也還未被全面地了解。因此,為了研究自旋電子的傳輸, 我們發展出一套製造並五苯平面有機自旋電子傳輸元件的技術。目前這套技術 已經趨於成熟,能讓我們將鐵磁電極及有機材料間的界面品質最佳化,並且確 保整個製備流程能在高真空的環境下完成。 雖然該平面有機自旋電子傳輸元件的樣品式樣已經能利用光刻和電子束曝光等 技術來完成,但有機半導體材料本身因為載子遷移率及帶電載子濃度低,使得 樣品電導率過低,導致測量上的困難。所以,我們使用鋁作為摻雜劑,試圖增 加元件的電導。截至目前為止,摻雜鋁之後的並五苯的電導可以提升到摻雜前 的三倍以上。除了電導外,我們也進行了該樣品之電性測量,包括在不同溫度 下的I-V曲線及場效應電晶體測量實驗。這些電性測量的實驗表現出帶電載子在 有機半導體和摻雜鋁的有機半導體內的傳輸特性。我們也分析了場效應電晶體 測量實驗結果,藉此了解摻雜劑如何影響並五苯在費米面附近的電子能帶結構。 此外,摻雜鋁之後的平面並五苯自旋電子元件在室溫下的局域磁阻也被觀察到 了。並五苯 5 nm 而鋁 0.1 nm 的摻雜比例下,該自旋電子元件的局域磁阻可以 達到 -0.7%。帶電載子傳輸過程保留的自旋訊號,讓這項平面有機自旋電子傳輸 元件的製備技術成為未來自旋電子傳輸機制研究的有力工具。

Spin injection and transport in organic semiconductors is a developing topic in the last ten years, and the detailed mechanics is not thoroughly understood yet. In order to investigate the spin transport mechanisms, we develop a technique to fabricate lateral pentacene spin transport devices. By far, the in situ fabrication techniques are well developed to make sure that the whole fabrication process is done under a high vacuum environment. On the other hand, to achieve higher con- ductance of the devices, we selected aluminum as the dopant. So far the conductance of Al-doped pentacene can be up to three times the value of the intrinsic pentacene. According to electrical transport measurement, the identicality of the electri- cal transport properties of pure pentacene and Al-doped pentacene, including the linearity feature of ln(G) − T 1/4 relation and the Poole-Frenkel form between the conductivity and electric field, indicates that the charge transport mechanism be- hind should be the same. The dopant only increases the carrier concentration of the organic semiconductor via charge transfer between the organic material and the metallic dopant, but does not change the electrical transport mechanism. We also analyze the experimental result of the FET measurement to understand how the dopant influence the band structure of pentacene near conducting region. Additionally, the local magnetoresistance -0.7% of the lateral Al-doped pentacene at room temperature is observed. The main contribution of our work is to make scientific demonstration that the poor conductivity of the organic materials can be improved with proper choice of metallic doping, while local magnetoresistance can still be observed in such system. Therefore, the in situ fabricated lateral pattern with metallic doped organic materials would serve as a suitable candidate for further researches on spin transport mechanism such as spin diffusion in organic semicon- ductors.