研究生: |
凃詠俊 Tu, Yung-Chun |
---|---|
論文名稱: |
側向單/多級串接氧化鋅奈米線與其異質結構於紫外光檢測器之研製 Fabrication of UV detectors based on laterally-oriented ZnO nanowires and n-ZnO/p-SnO (or p-CuO) nano heterojunctions |
指導教授: |
王水進
Wang, Shui-Jinn |
學位類別: |
碩士 Master |
系所名稱: |
電機資訊學院 - 微電子工程研究所 Institute of Microelectronics |
論文出版年: | 2011 |
畢業學年度: | 99 |
語文別: | 中文 |
論文頁數: | 69 |
中文關鍵詞: | 氧化鋅奈米線 、水熱法 、異質結構 、斜角 、紫外光檢測器 |
外文關鍵詞: | ZnO-NWs, HTG, heterojunction structure, tilted, UV sensors |
相關次數: | 點閱:76 下載:1 |
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本論文之研究主題係藉由水熱法(hydro-thermal growth, HTG)進行一維氧化鋅奈米線(ZnO nanowires, ZnO-NWs)之選擇性成長,並於奈米線上進行薄膜沉積進而製備出異質接面結構之UV光感測器。本論文主要研究工作概分為下列三個部份:
於第一部分中,我們利用黃光微影技術定義出多級串接元件的區域,並於其成長側向氧化鋅奈米線後再浸泡於稀釋的鹽酸溶液中30秒進行表面粗化工程,利用奈米線與奈米線相互疊接進行多級串接。我們比較單級串接至八級串接條件下不同的光電分析,實驗結果發現五級串接元件具有最好的UV光感測響應。此元件於UV光波長365 nm照射下有2.4倍的響應,所需的響應時間與回復時間分別是約10秒與32秒。
於第二部分中,我們將已成長垂直的氧化鋅奈米線置於傾斜75度角的載具,進行不同厚度(50、200、500與1000 nm) p-type SnO薄膜沉積,製備出異質接面結構的UV光感測器進行外觀型態及光電分析。實驗中所使用的傾斜角載具,可預防進行製作電極時p-SnO/基板形成短路的現象,進而完成我們所需要的異質結構的UV光感測器。實驗結果發現,四個不同p-type SnO厚度的異質結構UV光感測器展現出良好整流比與不同的光電特性。其中以沉積500 nm厚度的異質結構UV光感測器有最好的響應,此元件於UV光波長254 nm照射下有8.5倍的響應,所需的響應時間與回復時間分別是5秒20秒,其臨界電壓9V及漏電流強度3.8 A/cm2 ( Jr @ -5 V)。
於第三部分中,我們係以與第二部分相同之步驟進行垂直式氧化鋅奈米線之成長,之後利用旋轉塗佈技術將Polymethylmethacrylate (PMMA)填充於奈米線與奈米線間的間隙,並利用Inductively Coupled Plasma (ICP)進行PMMA蝕刻,使部分氧化鋅奈米線尖端未受PMMA包覆,進行不同厚度(300、600、900、1200與1500 nm)的p-type CuO薄膜沉積,製備出異質結構的UV光感測器進行外觀型態及光電分析。實驗中所使用的PMMA是絕緣且透光佳的材料,可預防進行製作電極時,上下電極形成短路的現象且其對UV光穿透至空乏區無顯著影響,進而完成我們所需要的異質結構UV光感測器;而五個不同p-type CuO厚度的異質結構UV光感測器亦展現出良好的整流比與不同的光電特性。其中以沉積1200 nm厚度的異質結構UV光感測器有最好的響應,此元件於UV光波長254及365 nm照射下分別有7.4倍與11.6倍的響應,在UV光波長365 nm下所需的響應時間與回復時間分別是3.5及3.5秒,其臨界電壓1.8 V及逆偏漏電流強度0.19 A/cm2 ( Jr @ -5 V).。
本研究以HTG製備出具有良好的高寬比之成長ZnO NWs,且研發出粗化工程及斜角沉積技術及填充透光率佳的絕緣材料技術,完成多級串接及異質結構的UV光偵測器元件,且其皆有很大的響應,響應時間與回復時間亦相當快速,預期在未來UV光偵測器元件應用上極具潛力與競爭力。
In this thesis, the growth and optoelectronic properties of ZnO nanowires-based nanoheterojunction and lateral structures are studied. The preparation of the ZnO nanowires (ZnO-NWs) using hydro-thermal growth (HTG) method and theirs applications in UV sensors are also investigated.
There are three parts comprised in this thesis. The first part focus on the design and fabrication of a series connection of lateral ZnO-NWs for nano optoelectronic sensors. The samples were placed in a solution of 0.04 M zinc nitrate hexahydrate and 0.04 M Hexamethylenetetramine at 90oC for 3 hours for the laterally growth ZnO-NWs between two neighboring electrodes. The device was further dipped into a dilute HCl solution (0.36%) for 30s to roughen the surface of ZnO-NWs. The photo induced currents of the lateral ZnO-NWs with or without series connections under UV light (254 and 365 nm, 6 mW/cm2) illuminations are presented and discussed. The UV sensor with five series connections shows a sensitivity (IUV/Idark) as high as 2.4 and a response time as low as 10~32 s.
The second part focuses on the use of a ZnO-NW-based nano heterojunction (NH) structure for optoelectronic sensors applications. Nano heterojunction arrays (NHAs) were formed via tilted sputtering deposition of p-type SnO onto the vertical-aligned ZnO-NWs grown by hydrothermal growth (HTG) method. The optoelectronic properties of the SnO/ZnO-NWs NHAs with SnO thicknesses (50, 200, 500, and 1000 nm) are analyzed. The fabricated p-SnO/n-ZnO-NWs NHAs with various SnO thicknesses all exhibit a well-defined rectifying behavior in darkness. Note that the sample with 500-nm-thick SnO film exhibits the highest forward current among all. It shows a diode-like behavior with a forward threshold voltage (Vth) of ~9 V, and a leakage current density (Jr @ -5 V) of 3.8 A/cm2). It indicates that the photo-induced current increases linearly with increasing the UV light power intensity. A distinctly increase in the photo-induced diode current of about 8.5 times under 6 mW/cm2 UV illumination was obtained.
In the third part of this thesis, the same HTG process for the synthesis of vertically aligned ZnO NWs was conducted. The samples were placed in a solution of 0.04 M zinc nitrate hexahydrate and Hexamethylenetetramine at 90°C for 1 hour. After HTG growth, the interspaces between ZnO-NWs were filled with PMMA by spin-coating. It was followed by an ICP dry etching to unveil the top portion of the ZnO-NW arrays. Then the different p-CuO thickness (300, 600, 900, 1200, and 1500 nm) was sputtered onto the vertical ZnO-NWs and the p-CuO/n-ZnO-NWs with PMMA padding NHJs are formed and the optoelectronic properties are studied. The use of PMMA which has superior transmittance UV light could avoid the collapse of vertically-aligned ZnO-NWs and effectively insulate the direct contact between top and bottom electrodes. All devices exhibit a well-defined rectifying behavior in darkness. Note that the sample with 1200-nm-thick CuO film exhibits the highest forward current among all. It shows a diode-like behavior with a forward threshold voltage (Vth) of ~1.8 V, and a lower leakage current density (Jr @ -5 V) of 0.19 A/cm2. Distinct increase in the photo-induced diode current of about 11.6 times and 7.4 times under UV light wavelength of 365 and 254 nm (identical power density of 6mW/cm2) UV illumination were obtained, respectively. The fast photoresponse times (rise time ~3.5 s and fall time ~3.5 s) indicate that the p-CuO/n-ZnO-NW NHJ arrays have good optoelectronic properties. In addition, the reversible cycles of the photoresponse curve suggests a stable and repeatable operation of photo detecting and optical sensing.
It is expected that HTG of ZnO-NWs which are with the merits of high aspect-ratio could be a potential material for the applications in UV sensors. Furthermore, the functional ZnO-NWs-based nanoheterojunction structures would offer a simple and low-cost building block for high-performance optoelectronics in the near future.
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