透明導電薄膜同時具有高光學穿透率與高導電率這兩種優異的特性，因此被廣泛應用於各種光電元件，如太陽能電池、液晶顯示器和發光二極體等。本論文利用光導天線與雷射光激發電漿之兆赫波時域光譜儀研究透明導電氧化物薄膜(氧化銦錫、摻鋁氧化鋅與摻鋁鐿氧化鋅)在不同薄膜厚度下於兆赫波段的光學常數與導電率。
這三類透明導電薄膜在0.1-2.4THz波段的光學與電性參數經由整合光導天線與雷射光激發電漿兆赫波時域光譜儀量測結果分析而得。結合傅立葉轉換紅外線光譜量測，我們可得到這些薄膜的廣域穿透率(0.1-15THz)。舉例而言，100奈米厚的氧化銦錫、摻鋁氧化鋅與摻鋁鐿氧化鋅薄膜在兆赫波段的穿透率分別約為21%、41%和28%。由這些材料的複數折射率計算得到的寬頻的複數導電率可以Drude-Smith模型擬合之，進而得到其電性參數如直流遷移率、載子濃度與直流導電率。經由分析，氧化銦錫薄膜的直流遷移率與導電率分別為96-120cm2V-1s-1和1.18-1.65×103Ω-1cm-1；摻鋁氧化鋅薄膜者為7-84 cm2V-1s-1和0.41-1.06×103Ω-1cm-1；摻鋁鐿氧化鋅薄膜者為26-85 cm2V-1s-1和0.91-1.12×103Ω-1cm-1。我們也用X光繞射分析這些樣品，當薄膜中晶粒越大時遷移率隨之變大，但當其載子濃度較高時，遷移率受摻雜離子間的平均自由路徑較小的影響而變低。結晶性會隨薄膜厚度增加而變佳，300nm厚之氧化銦錫薄膜更由非晶相轉為多晶相。本論文的實驗結果指出所研究之摻鋁氧化鋅薄膜與摻鋁鐿氧化鋅薄膜的電性參數略差於氧化銦錫薄膜但兆赫波段的穿透率較好。這三種薄膜的電性參數的差距可由晶粒大小、結晶相與載子濃度討論之。

The transparent conductive oxides (TCOs, indium-tin oxide (ITO), aluminum-doped zinc oxide (AZO), aluminum and ytterbium-doped zinc oxide (AYZO)) thin films which exhibit outstanding properties such as high transparency in the visible region and good electrical conductivity are measured by terahertz time-domain spectroscopy (THz-TDS) based on photoconductive (PC) antenna and laser-induced air-plasma. The optical and electrical properties of these TCO thin films in the THz frequency range (0.1-2.4THz) are obtained. Broadband optical and electrical characteristics can be determined by combing the results from THz-TDS based on PC antenna and laser-induced air-plasma, respectively. The frequency-dependent complex refractive indices have been extracted from the TDS measurements. Complex conductivities of the TCO samples can then be determined. Together with Fourier transform infrared spectroscopic (FTIR) measurements, we’ve found that the THz and far-infrared transmittance of 100 nm-thick ITO, AZO, and AYZO thin films are ~21%, ~48%, and ~28%, respectively. By fitting complex conductivities of the TCOs with the Drude-Smith model, electrical properties such as DC mobility (μ), carrier concentration (Ne), and DC conductivity (σDC) are obtained. Here, μ and σDC for ITO thin films are 96-120cm2V-1s-1 and 1.18-1.65 ×103Ω-1cm-1, respectively. For AZO and AYZO thin films, these parameters are 7-84 cm2V-1s-1 and 0.41-1.06×103Ω-1cm-1 versus 26-85 cm2V-1s-1 and 0.91-1.12×103Ω-1cm-1, respectively. We have also examined structural and crystalline properties of samples by X-ray diffraction (XRD) measurements. From the XRD information, it can be concluded that motilities can be enhanced as increasing grain size, but reduced with overly high carrier concentration because of the smaller distance between impurity ions.

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