Please use this identifier to cite or link to this item:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/52418
Title: | 石墨烯/氧化金/矽複合結構分析及其於光偵測元件的應用研究 Analysis and application of Graphene/AuOx/Si heterojunction for photodetection |
Authors: | Tai-Chi Yang 楊泰騏 |
Advisor: | 陳學禮(Hsuen-Li Chen) |
Keyword: | 氧化金,石墨烯,內建電場,光偵測元件,光電壓響應度,寬波段偵測,光通訊波段,長期穩定, gold oxide (AuOx),graphene,built-in electric field,photodetector,photovoltage responsivity,broadband detection,spectral regime of optical telecommunication,long-term stability, |
Publication Year : | 2015 |
Degree: | 碩士 |
Abstract: | 本論文利用反應性濺鍍的方式製作出氧化金薄膜,並透過各種材料分析的方法來量測薄膜的性質:利用光譜儀和橢圓偏光儀得到了氧化金的光學性質,其相較於金明顯較透光、折射率高(2.4-2.6),消光係數小(0.1-1)。利用掃描式電子顯微鏡、X射線光電子能譜和片電阻量測結果可以推測剛製作好的氧化金化學組成可能是或接近於三氧化二金,但在大氣下放置一段時間會部分還原而產生金奈米粒子,表示氧化金並不穩定。利用紫外光光電子能譜可以得到氧化金的價帶最大值位置低於費米能階0.42電子伏特和功函數值約為5.8電子伏特,表示氧化金是一個功函數很大的半導體材料。而接著從氧化金的消光係數可以計算出氧化金的光學能隙大約為0.87電子伏特,且在更小光子能量波段仍有吸收,可能是因為部分還原的金和氧空缺的存在而使氧化金存在許多中間能階。綜合前面的結果可以得到氧化金的大致能帶圖。
為了瞭解氧化金與石墨烯的接面特性,我們利用聚甲基丙烯酸甲酯作為介質將石墨烯轉置到氧化金薄膜上,利用霍爾量測系統分析石墨烯的電性,發現石墨烯會被氧化金強烈的p型摻雜,片電阻減少89.2%,比其他分子摻雜的效果要強。經由X光繞射儀、X射線光電子能譜與穿透式電子顯微鏡的分析,證實石墨烯可以減少氧化金的還原。在高解析穿透式電子顯微鏡的分析下,發現在氧化金與矽的介面會有氧化矽薄層的產生,在後續元件的偵測機制中扮演著重要的角色。 由於氧化金與矽的接面會有強烈的內建電場,有助於載子的分離,本研究因此製作了氧化金/矽以及石墨烯/氧化金/矽複合結構的光偵測元件,量測短路電流(低耗能)和開路電壓(低產熱)在照光前後的變化,兩個元件都是較適合在電壓模式下操作,主要是因為氧化金的電阻值大和生成氧化矽薄膜的隔絕會將載子束縛在氧化金內部和氧化矽兩側,此外有石墨烯覆蓋的元件效率比沒有石墨烯的大很多,這是因為石墨烯可以減緩氧化金的還原與提高載子的傳導速度,光電壓響應度最大可到8230伏特每瓦,且可在弱光下操作(大約0.03飛瓦每平方微米)。另外此元件還能夠在矽不吸收的波段工作,主要是藉由石墨烯與氧化金的吸收,光電壓響應度最大可到102伏特每瓦,具備寬波段偵測的能力(波長260-1800奈米的波段)。此元件在大氣下放置四個月之後,在偵測效率表現上和剛製作完的元件非常接近,擁有長期穩定的優點。 We used the reactive magnetron sputter to deposit gold oxide (AuOx) film and analyzed the properties of gold oxide films by using several material characteristic methods. By spectrophotometer and ellipsometer, we obtained the optical properties of gold oxide, which had larger transmittance, larger refractive index (2.4-2.6), and lower extinction coefficient (0.1-1) than gold film. By scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and sheet resistance measurements, we suggested that the as-grown gold oxide film might be Au2O3, which would reduce and form gold nanoparticles for a while, implying the gold oxide films were unstable. By ultraviolet photoelectron spectroscopy (UPS) measurement, we found the valence band maximum is below the Fermi level by 0.42 eV and the estimated work function is 5.8 eV, which means the gold oxide in this study is a high-work-function semiconductor. We also calculated the energy bandgap from the extinction coefficient and the value of optical bandgap is ca. 0.87 eV. However, there was still some absorption below 0.87 eV of photon energy since the gold oxide might reduce to form gold and generate oxygen vacancies, which would create some intermediate states in it. From the above analysis results, we could obtain the band diagram of gold oxide. To study the properties of the junction between gold oxide and graphene, we transferred a graphene layer onto gold oxide film by PMMA-mediated method. By using Hall Measurement System, we found graphene could be heavily p-type doped by gold oxide film and the sheet resistance of doped graphene was decreased by 89.2%, which was larger than using other doping materials. By X-ray diffraction instrument (XRD), XPS, and transmission electron microscope (TEM), we found graphene could retard the reduction process of gold oxide films. By high resolution transmission electron microscope (HRTEM) observation, we could find there was thin SiOx layer formed between gold oxide and silicon, which would play an important role in the following AuOx-based devices. Since there is strong built-in electric field between gold oxide and silicon, which can assist the separation of carriers, we fabricated AuOx/Si and graphene/AuOx/Si heterostructure based photodetectors. We measured the change of short-circuit current (low power consumption) and open-circuit voltage (low heat generation) of the devices before and after illuminating of broadband light, and both devices had better detection efficiency in photovoltage mode. We suggested the high resistance of gold oxide and the thin separation layer of SiOx would confine carriers in gold oxide and at two sides of thin SiOx layer. In addition, graphene/AuOx/Si performed much better detection efficiency than the AuOx/Si device since graphene can effectively retard the reduction process of gold oxide and improve the transportation of carriers. The measured photovoltage responsivity could reach 8230 V/W, and the device could also work under low light power density (ca. 0.03 fW/μm2). Furthermore, the graphene/AuOx/Si device could also work in the spectral regime of optical telecommunication which Si could not absorb the incident light but that could be absorbed by graphene and gold oxide, and the measured photovoltage responsivity could reach 102 V/W; therefore, the device had broadband detection ability (260-1800 nm wavelength). After stored for 4 months, the device remained almost the same detection efficiency, which performed long-term stability. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/52418 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 材料科學與工程學系 |
Files in This Item:
File | Size | Format | |
---|---|---|---|
ntu-104-1.pdf Restricted Access | 10.28 MB | Adobe PDF |
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.