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標題: | 新穎奈米材料與單根二氧化錫一維奈米線組成之複合元件之光電導增強現象之研究 Enhanced photocurrent phenomena of composites consisting of one-dimensional single SnO2 nanowire and novel nanostructure materials |
作者: | Meng-Lin Lu 呂孟霖 |
指導教授: | 陳永芳 |
關鍵字: | 二氧化錫奈米線,硒化鎘量子點,銅銦硫量子點,氧化鎳奈米粒子,鐵磁性材料,鎳薄膜,光電流,光電流增益,光檢測器, SnO2 nanowire,CdSe quantum dot,CuInS2 quantum dot,NiO nanoparticle,ferromagnetic material,nickel thin film,photocurrent,photocurrent gain,photodetector, |
出版年 : | 2012 |
學位: | 博士 |
摘要: | 在本論文中,我們主要研究的方向為由化學氣相沉積法(CVD, chemical vapor deposition)製造出的二氧化錫一維奈米線(nanowire)與其他各式樣奈米材料所組合而成複合物奈米元件之光電導(photoconductivity)的特性。在奈米尺度下由於較高的表面積對體積的比值,奈米線表面的狀態將會對光電導產生巨大的影響,因此我們得以發現巨大的光電流增益,超越了所有先前的文獻報導。本論文包含了四大主題,其摘要如下:
1. 硒化鎘量子點與二氧化錫奈米線組成的複合材料之光電導特性 二氧化錫是寬能隙的半導體材料,其能隙大約為3.6 eV,一般來說此半導體材料只吸收大於其能隙的光子,而硒化鎘量子點的能隙大約在可見光的範圍。將硒化鎘量子點均勻的鋪在奈米線表面後,很有趣的,不只大於其能隙的光子激發此複合型材料後光電流增益(photocurrent gain)會顯著的提升,而在小於其能隙的光照射後,由於硒化鎘量子點的電子電洞對仍會被激發出來,所以此複合材料之光電導也會有想當程度的變化。主要的機制來自於硒化鎘量子點與二氧化錫奈米線的能帶結構是第二型的能帶結構(type II band alignment),而此能帶結構在經由光激發後將會有載子由量子點傳輸到奈米線上的情形。我們相信這種奈米複合型材料是一個嶄新的方法去增加光檢測器(photodetector)的效率也可以增加其檢測器的感應範圍。 2. 銅銦硫量子點與二氧化錫奈米線組成的複合材料之光電導特性 承接主題一,我們將硒化鎘量子點置換成無毒性的銅銦硫量子點,驚奇的是我們用可見光雷射激發此複合性材料後,光電流增益可以大大的提高,甚至比原本單純二氧化錫奈米線在紫外光雷射照射時還要大。而主要的機制也是來自於量子點與二氧化錫奈米線的能帶結構是第二型的能帶結構(type II band alignment),所以也會有載子由量子點傳輸到奈米線上的情形。為了詳細探討其機制,在這個主題中我們用了三種不同條件的銅銦化硫量子點來做比較,第一種是鋅銅銦硫/硫化鋅核-殼結構量子點,第二種是鋅銅銦硫核量子點,第三種是銅銦硫核量子點。我們再利用吸收光譜儀,時間解析光譜儀,X射線光電子能譜儀來詳細探討載子傳輸的機制,而透過這兩種新穎材料的結合,我們可以有個更好的方法來製造超高效率的光檢測器原件。 3. P型半導體氧化鎳奈米粒子與n型半導體二氧化錫奈米線組成的複合材料之光電特性 本實驗中,我們將氧化鎳此p型半導體材料的奈米粒子沉積在二氧化錫n型半導體的奈米線上。由於兩個材料介面是一個p-n的異質接面,形成的內建電場將會使奈米線表面的能帶向上彎曲而使得奈米線表面高電阻區域的空乏區增加然後其暗電流(dark current)將明顯的降低。當雷射照射到此複合材料後,其光電流增益因為表面能帶彎曲(surface band bending)的效應,也會有明顯的增加。透過一些理論模擬,我們成功的提出合理的機制以及解釋了此有趣的現象,相信這個物理現象能夠提升光檢測器原件的效率。 4. 鐵磁性材料鎳電極與二氧化錫奈米線的光檢測器之光電特性 這個主題中,我們使用了鐵磁性材料鎳的薄膜當做二氧化錫奈米線的電極。由於鎳薄膜經過磁場磁化後即使將外加磁場移開,此薄膜仍然有殘磁的存在,而此磁場將會對我們奈米尺度下的裝置造成可觀的影響。我們在垂直基板表面的方向給予一個外加磁場磁化我們的複合型材料,很有趣的,隨著磁化的磁場增加其暗電流也隨之減少,當光照射之後,其光電流將會顯著的提高。計算出其光電流增加倍率可達到2000%以上,我們提出了機制來解釋磁場造成載子傳輸的現像改變,使得影響氧化物半導體奈米線光電流的兩種現象(i)表面氧分子吸附作用(ii)表面能帶彎曲作用,大大的提升其影響程度,進而其光電流將會顯著的提升。我們相信此有趣的效應將可以簡單的實際應用在各種光電元件上,成為一個很實用的技術來提升裝置的效率。 In this thesis, we report the study of optoelectric properties of single SnO2 nanowire devices, which have been integrated with several novel nanostructure materials. Due to a large surface to volume ratio of nanomaterials, the coupling strength between the constituent elements can be greatly enhanced. It therefore provides us an excellent opportunity to discover giant photocurrent gain in our newly design nanocomposite devices, which sets the highest record for the devices based on the single semiconductor nanowires. The highlight of our scientific achievement is briefly described as follows. 1. Enhanced photocurrent gain and spectrum range based on the composite consisting of SnO2 nanowires and CdSe quantum dots High sensitivity with additional spectral response based on the composite consisting of SnO2 nanowires and CdSe quantum dots has been demonstrated. The underlying mechanism is attributed to the spatial separation of photogenerated electrons and holes due to the charge transfer arising from type II band alignment between CdSe quantum dot and SnO2 nanowire. This work shows that by selective decoration of suitable quantum dots, the photocurrent gain of nanowires not only can be greatly enhanced, but also can be extended to a wider range photoresponse spectrum. Our result, therefore, provides a very useful guideline to create high efficiency photodetectors. 2. Photodetectors with ultrahigh gain and wide spectral response based on the composite consisting of I-III-VI quantum dots and single SnO2 nanowire Photodetectors with ultrahigh sensitivity and wide spectral response based on the composites consisting of I_III_VI semiconductor quantum dots decorated onto single SnO2 nanowire have been demonstrated. Under the illumination of an Argon laser (488 nm) with the photon energy smaller than the band gap of SnO2 nanowire, remarkably, an ultrahigh photocurrent gain up to 4000 folds can be achieved. The underlying mechanism is attributed to the spatial separation of photogenerated electrons and holes due to the charge transfer arising from the type II band alignment between quantum dots and SnO2 nanowire. This work thus shows a new approach that by selectively decorating suitable quantum dots, the photocurrent gain of SnO2 nanowires can be greatly enhanced and extended to a wide range of photoresponse spectrum previously inaccessible. The result with associated mechanism thus provides a very useful guideline to create cheap, non-toxic and highly efficient photodetectors. 3. Large enhancement of photocurrent gain based on the composite of a single n-type SnO2 nanowire and p-type NiO nanoparticles The high sensitivity of photodetector in the UV range based on the composite consisting of a single SnO2 nanowire and NiO nanoparticles has been demonstrated. The underlying mechanism is attributed to the formation of p-NiO and n-SnO2 heterojunction on the nanowire surface. The enhanced space charge region owing to the existence of p-n heterojunction increases the surface electric field, which will improve the separation of photogenerated electrons and holes, and the photoresponse gain will be greatly enhanced. This work shows a new approach that by decorating suitable p-type nanoparticles on n-type nanowires, the photoresponse gain can be enhanced drastically. Our result should be useful for creating novel high efficiency photodetectors. 4. Ultrahigh-gain single SnO2 nanowire photodetectors arising from ferromagnetic nickel electrodes We report the first attempt of magnetic manipulation of photoresponse in an one-dimensional (1D) device, in which a highly sensitive photodetector in the UV region composed of tin oxide nanowire (SnO2 NW) and ferromagnetic nickel (Ni) electrodes have been fabricated and characterized. Surprisingly, as the Ni electrodes were magnetized, the photocurrent gain can be greatly enhanced by up to 20 times, which is far beyond all of the previously reported enhancement factors for the functionalized nanowire photodetectors. The underlying mechanism is attributed to both oxygen molecules adsorbed and surface band bending effects due to the migration of electrons to the surface of SnO2 NW caused by the magnetic field of ferromagnetic electrodes. The novel approach presented here can pave a new route for the creation of highly efficient optoelectronic devices based on the coupling between ferromagnetic materials and nanostructured semiconductors. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/65134 |
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