透過您的圖書館登入
IP:3.235.180.245
  • 學位論文

石墨烯在兆赫波段光電特性之量測及其在兆赫波段液晶相位調制器之應用

Characterization of Graphene Layers in Liquid Crystal Terahertz Phase Shifters

指導教授 : 潘犀靈

摘要


石墨烯同時具有優異的光學穿透率、導電率以及載子遷移率等特性,使得它有相當高的潛力可以廣泛應用於各種元件,包含高功率元件、光電感應器,兆赫波段元件等。在本論文中我們研究利用石墨烯製作於兆赫波段的液晶相位調制器。 我們藉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獲得單層與雙層石墨烯薄膜在0.2 - 1.4 THz 波段的光學穿透係數,並分析之可得到樣品之寬頻複數導電率。利用Drude自由電子模型(Drude free-electron model)擬合可進而獲取其電性參數,諸如電漿頻率、散射時間、載子遷移率,以及直流導電率。相比另一種兆赫波段透明電極,銦錫氧化物奈米晶鬚(Indium-tin-oxide nanowhiskers),石墨烯的穿透率較低,但是具有更高的導電率以及載子遷移率。 接著,我們利用石墨烯作為透明電極製作兆赫波段相位調制器,並以光導天線兆赫波時域光譜儀量測其調制相位隨外加電壓的變化。施加約莫2.2伏特的偏壓於石墨烯相位調制器即可改變1.0 THz的訊號達相位π/2,相較之下,早先研究的銦錫氧化物奈米晶鬚相位調制器則需要約5.6伏特才可達到相位π/2。另一方面,我們使用多夾層結構提升銦錫氧化物奈米晶鬚相位調制器達相位2π調控,其工作電壓約為2.6伏特。此工作電壓可與薄膜電晶體以及互補式金屬氧化物半導體技術相匹配。我們用來擬合實驗數據的液晶隨電壓偏轉模型,理論趨勢與實驗結果非常相符。

關鍵字

兆赫波 石墨烯 液晶 相位調制器

並列摘要


The graphene sheet, which exhibits outstanding properties, such as high transparency in both visible and terahertz (THz) regions and superb electrical conductivity, are measured by terahertz time-domain spectroscopy (THz-TDS) based on photoconductive (PC) antenna and laser-induced air-plasma, respectively. The optical and electrical properties of monolayer and bilayer graphene films in the THz frequency range of 0.3~ 1.4 THz are investigated. Complex conductivities of the graphene samples can be extracted from the TDS measurements and fitted with the Drude free-electron model. Electrical properties of the samples, such as plasma frequency (ωp), scattering time (τ), dc mobility (μ), and dc conductivity (σ0), are obtained. Comparing to the indium-tin-oxide nanowhiskers (ITO NWhs), another promising candidate as transparent conductor for THz optoelectronic devices, graphene has lower transmittance but much higher conductivity and mobility. Furthermore, we have constructed and characterized THz phase shifters based on liquid crystals (LCs) with graphene grown by chemical vapor deposition (CVD) and indium-tin-oxide nanowhiskers (ITO NWhs) obliquely evaporated by electron-beam glancing-angle deposition (GLAD) as transparent conducting electrodes. A graphene-based phase shifter can achieve a phase shift of π/2 at 1.0 THz with the operating voltage of ~2.2 V (rms) versus ~ 5.6 V (rms) for ITO-NWhs-based phase shifter in previous work. On the other hand, 2π phase shift at 1.0 THz was achieved in an ITO-NWhs-based phase shifter with a multi-sandwiched structure by applying ~2.6 V (rms). The low operation voltage of both two kinds of phase shifters imply the compatibility with thin-film transistor (TFT) and complementary metal-oxide-semiconductor (CMOS) technologies. The experimental results of phase shifters are in good agreement with the theoretical predictions.

並列關鍵字

terahertz graphene liquid crystal phase shifter

參考文獻


[56] Y.-S. Lee, Principles of terahertz science and technology: springer, 2009.
[20] X. W. Lin, J. B. Wu, W. Hu, Z. G. Zheng, Z. J. Wu, G. Zhu, et al., "Self-polarizing terahertz liquid crystal phase shifter," Aip Advances, vol. 1, Sep 2011.
[22] Y. Wu, X. Z. Ruan, C. H. Chen, Y. J. Shin, Y. Lee, J. Niu, et al., "Graphene/liquid crystal based terahertz phase shifters," Optics Express, vol. 21, pp. 21395-21402, Sep 9 2013.
[10] R. Kohler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, et al., "Terahertz semiconductor-heterostructure laser," Nature, vol. 417, pp. 156-159, May 9 2002.
[3] J. H. Strait, P. A. George, M. Levendorf, M. Blood-Forsythe, F. Rana, and J. Park, "Measurements of the Carrier Dynamics and Terahertz Response of Oriented Germanium Nanowires using Optical-Pump Terahertz-Probe Spectroscopy," Nano Letters, vol. 9, pp. 2967-2972, Aug 2009.

延伸閱讀