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標題: | 石墨烯品質之快速非破壞性檢測及其光偵測元件之光收成增益研究 Rapid and nondestructive characterization of the structural quality of graphene and techniques for enhancing light harvesting in graphene based photodetectors |
作者: | En-Yun Wang 王恩芸 |
指導教授: | 陳學禮 |
關鍵字: | 石墨烯品質檢測,衰減全反射法,光學非均向性,快速非破壞性及高訊號對比檢測架構,石墨烯矽基光偵測元件,廣角度寬波段光收成結構, metrology of graphene quality,attenuated total reflection (ATR),rapid nondestructive and high contrast sensing system,graphene/silicon Schottky junction type photodetector,broadband and omnidirectional antireflective structures, |
出版年 : | 2014 |
學位: | 碩士 |
摘要: | 由於石墨烯從可見光至紅外光波段的穿透率極高,同時具有極佳的導電性,當石墨烯與矽晶圓接合時,石墨烯可視為高穿透性的透明導電膜,在接面處產生內建電場成為蕭特基接面。為了建立光電轉換效率優良的石墨烯�矽蕭特基接面光電元件,確認石墨烯的品質為首要的關鍵,品質良好的石墨烯具有較佳的導電率,並直接影響元件接面的電性。因此本篇論文中的第一部分,我們利用衰減全反射法(Attenuated Total Reflection, ATR)快速檢測石墨烯的品質及層數。根據石墨烯獨特的二維奈米結構造成的光學性質,用以分析石墨烯的品質、光學非均向性(optical anisotropy)與ATR反射圖譜的關係,並藉由實驗統整石墨烯的層數和品質的優劣程度於ATR反射圖譜中反射最低點的變化趨勢,證實ATR量測系統有潛力成為快速、高檢測訊號對比、非破壞性、大面積的石墨烯品質光學檢測方法。
光電元件的效率除了取決於接面的電性優劣之外,元件的光收成效果亦為重大的關鍵。因此如何有效降低反射、增加元件的吸收比例是增益元件效率的主要議題。於本篇論文的第二部分,我們首先製備穩定的石墨烯�矽蕭特基接面光偵測元件,再分別利用兩種方法來製作能夠增加光收成的奈米結構,改變元件表面的光學行為,進而達到寬波段、廣角度的抗反射效果,提升元件的光偵測能力。 第一種方法為運用介電質奈米粒子在元件表面堆疊具有漸變折射率性質的奈米粒子光學薄膜。此結構不但具有良好的寬波段抗反射性能,也不會對石墨烯造成破壞,使元件的外部量子效率於寬波段、廣角度均能夠大幅提升,最高能達到90%以上,而偵測率(detectivity)則能提升至2.76×〖10〗^13 (Jones),於波長850奈米單波長光源的偵測極限甚至能低達0.16 (nW/cm2)。另外我們亦以介電質奈米粒子建構出具有散射行為之抗反射結構。除了廣角、寬波段的抗反射效果之外,藉由光程的增加,此結構於長波段能夠產生額外的光收成及元件效率貢獻。 第二種方法為利用金侵入蝕刻法(Intruded Gold Nanoclusters, INC)在矽基板表面快速地蝕刻出淺、小、密集的奈米柱結構,藉由改變矽基材表面的光學行為來達到元件整體抗反射的效果。從電性量測結果中,能證實矽基板在經過蝕刻後仍然能與石墨烯建立電性良好的蕭特基接面。基於其寬波段低於5%的反射值,以及極低的暗電流,元件的外部量子效率最高能超過90%,而偵測率(detectivity)則能達到2.4×〖10〗^13 (Jones)。由於上述兩種抗反射結構的建構方法均能有效達到廣角、寬波段的抗反射功能,元件的光偵測能力不但在寬波段範圍內均能有效提升,偵測光源的入射角也不會影響光偵測的準確性。 Based on the prominently high optical transmittance and outstanding electrical properties, graphene could behave as a transparent electrode, and is able to construct Schottky junction after combing with semiconductor substrates. In order to develop well performed graphene/silicon Schottky-type devices, the quality of graphene should be carefully characterized. In the first part of this thesis, we utilize the attenuated total reflection (ATR) method to analyze the structure quality of graphene. Due to the two-dimensional nanostructure, graphene possesses evident optical anisotropic feature as long as the structure is intact. Making use of this unique optical property, we determined the structural characteristics of graphene by measuring the variation of its optical behaviors under transverse magnetic (TM) polarized light through ATR method. We concluded that as the defect density in graphene increases, the position of reflection dip in SPR reflection curve would move to larger angle with higher reflectance. We also demonstrated that ATR method has the potential to be a rapid, nondestructive, large scale, and great inspection contrast metrology on graphene samples. To improve the photoelectric conversion efficiency of graphene/silicon based photodetectors, light harvesting is a very important issue. In the second part of this thesis, we introduced dielectric nanoparticles (NPs) to construct omnidirectional antireflective structures. According to the experimental results, the external quantum efficiency (EQE) reached to more than 90% and the detectivity (D*) increased to 2.76×〖10〗^13 (Jones) at zero external voltage bias after adding the NP stack with optical gradient profile. Furthermore, the detection limitation could be lower than 0.16 (nW/cm2) at the wavelength of 850 nm. In the third part of this thesis, we transferred single layer graphene onto nano-textured silicon surface, which was rapidly fabricated by the intruded gold nanoclusters (INC) and metal assisted chemical etching (MAE) approaches. Taking advantage of the broadband and omnidirectional antireflective properties of the nanostructures, the reflection loss of the graphene/silicon Schottky-type photodetector was sufficiently suppressed to lower than 5%. Moreover, it is proved that the etching method caused little harm to electrical properties of device, thus the EQE could be significantly improved to more than 90%, and the detectivity (D*) increased to 2.4×〖10〗^13 (Jones) due to the low leakage current. The above-mentioned antireflective treatments demonstrated a great promise in developing high efficiency photodetectors in a broad wavelength region with omnidirectional light harvesting property. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/56447 |
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顯示於系所單位: | 材料科學與工程學系 |
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