以硒化鎘/硫化鋅與金奈米粒子建構先進之光感測元件

Abstract

在本論文中，吾人使用硒化鎘/硫化鋅(核/殼)和金奈米粒子，透過離子作用力建構多層光感測奈米元件結構於矽基板上。一個具較大能隙的硫化鋅如同硒化鎘奈米粒子的保護層，用以提高其穩定性和量子效應。由紫外-可見光吸收光譜和螢光光譜的結果顯示，硒化鎘/硫化鋅 奈米粒子比先前所使用的硒化鎘奈米粒子具較好的光特性。 在結合硒化鎘/硫化鋅和金奈米粒子的四層奈米結構中，在照射375 nm雷射光後，在各種偏壓下有固定約28 nA (30μm / 5μm) 與 70 nA (30μm / 15μm) 的電流增加。除了375 nm，亦利用400 nm和435 nm的雷射作為激發光源，我們發現在較短波長照射下，將產生較大的光電流，此結果亦與吸收 / 放射光譜相互印證。此外，較長的電極長度或較多層之奈米結構將導致更大的光電流產生，可以利用“奈米蕭特基二極體和電阻陣列”模型成功地解釋之，我們可以利用HSPICE去模擬此二維模型且發現有同樣的現象。最後，我們發現四層的 金 / 硒化鎘/硫化鋅 奈米結構之“每單位體積所產生的光電流”至少為硒化鎘薄膜結構的1183倍，且在我們理想的推論下，其光電轉換效率可達40%。 除了結合金和硒化鎘/硫化鋅奈米粒子的結構，吾人單單利用硒化鎘/硫化鋅奈米粒子建構多層結構於矽基板上。在執行離子的組裝製程之前，MSA-硒化鎘/硫化鋅與AET-硒化鎘/硫化鋅奈米粒子表面分別利用化學法修飾成帶負電荷和正電荷官能基。我們發現十二層的結構之“每單位體積所產生的光電流”至少為傳統硒化鎘薄膜結構的34倍。最後，我們推斷 金 / AET-硒化鎘/硫化鋅 奈米元件如同一光二極體，然而 MSA-硒化鎘/硫化鋅 / AET-硒化鎘/硫化鋅奈米元件如同一般傳統的光敏電阻。此外，金 / AET-硒化鎘/硫化鋅 奈米元件是一個具強大潛力可以發展作為太陽能電池之應用。

In this work, we used CdSe/ZnS (core/shell) and/or Au NPs to construct the multi-layered photo-sensing nanodevice structures on a silicon substrate through ionic interaction. ZnS with larger energy bandgap served as a passivation layer on CdSe NPs to enhance the stability and quantum yield. From the results of UV-visible absorbance and photoluminescence spectra, CdSe/ZnS NPs exhibit better optical properties than CdSe NPs in the previous work. For the four-layered nanostructure composed of CdSe/ZnS and Au NPs, there was constantly about 28 nA (30μm / 5μm) and 70 nA (30μm / 15μm) increment to the current measured in the dark for each voltage bias after illumination with 375 nm laser. In addition to 375 nm, 400 nm and 435 nm lasers were also used as light sources for photo-excitation. We found that more photocurrent was generated under shorter wavelength illumination, which was also verified in the absorption / emission spectra. Besides, more photocurrent was generated in the nanostructure with a longer length or a larger number of layers, which can be successfully explained by using the model of “nano-Schottky-diodes and resistor array”. We can obtain the same phenomenon as using HSPICE to simulate the two dimensional model. Finally, we found that the“photocurrent volume density (PVD)”of the 4-layered Au / AET-CdSe/ZnS nanostructure is at least 1183 times better than that of CdSe thin film structure. The power conversion efficiency can achieve 40% based on ourideal inference. In addition to nanodevice composed Au and CdSe/ZnS NPs, we constructed multi-layered structure on the silicon oxide substrate by using only CdSe/ZnS NPs. MSA-CdSe/ZnS and AET-CdSe/ZnS NPs, which were chemically modified prior to ionic assembly process, have negative-charged and positive-charged functional groups on the surface of the NPs respectively. We found that the PVD of the 12-layered structure is at least 34 times better than that of conventional CdSe thin film structure. Finally, we conclude that the Au / AET-CdSe/ZnS nanodevice acts like a photodiode while the MSA-CdSe/ZnS / AET-CdSe/ZnS nanodevice acts like a typical traditional photoresistor. Besides, the Au / AET-CdSe/ZnS nanodevice has enormous potential to turn into solarcells applications.