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標題: | 利用原子層沉積技術成長氧化鋅薄膜與奈米結構應用於發光二極體之研究 Applications of ZnO Thin Films and Nanostructures grown by Atomic Layer Deposition on Light-Emitting Diodes |
作者: | Ying-Tsang Shih 施穎蒼 |
指導教授: | 陳敏璋 |
關鍵字: | 原子層沉積技術,氧化鋅,奈米點,發光二極體, atomic layer deposition (ALD),zinc oxide (ZnO),nanodots,light-emitting diode (LED), |
出版年 : | 2010 |
學位: | 博士 |
摘要: | 在本論文,我們利用原子層沉積技術成長高品質氧化鋅(ZnO),其型態包含ZnO薄膜與ZnO量子點,並將此ZnO化合物應用於發光二極體中。
首先,我們將氧化鋅薄膜成長於p型碳化矽(SiC)基板上,分別製作出n-ZnO/p-SiC與n-ZnO/i-ZnO/p-SiC兩種不同結構之異質接面發光二極體。n-ZnO/p-SiC元件主要由SiC的缺陷產生可見光波段的光譜。藉由在n-ZnO和p-SiC之間夾入一層無摻雜且具有低載子濃度的的i-ZnO層,可以促使來自ZnO的電子與來自SiC的電洞注入i-ZnO層,成功製作出發光波長為紫外光的n-ZnO/i-ZnO/p-SiC異質接面發光二極體。 我們將ZnO成長於SiO2奈米顆粒間的孔隙中,藉由熱處理製作出均勻分布在SiO2孔隙間的ZnO量子點,利用光學性質探討此量子點所造成的能帶藍移效應,並且將此奈米結構成長於氮化鎵(GaN)基板上製作發光二極體。藉由SiO2與ZnO的奈米混合物(SiO2-ZnO nanocomposite)所提供的低折射率,使得n-ZnO/SiO2-ZnO nanocomposite/p-GaN發光二極體可以在1mA的電流灌注下,發出明顯的紫外光。接著利用類似結構,將ZnO與SiO2-ZnO nanocomposite製作於p型氮化鋁鎵(AlGaN)基板上,製作出n-ZnO/SiO2-ZnO nanocomposite/p-AlGaN結構,在電流灌注下,得到超線性上升的紫外光電激發光,有效提高元件的效率。 接著我們利用原子層沉積技術將高品質ZnO薄膜成長在非晶質的康寧1737玻璃基板上。藉由夾入在300°C下成長,並且預先熱處理過的ZnO緩衝層,可以在150°C的低溫下,成長出高品質ZnO薄膜,此ZnO薄膜具有高度(0001)方向結晶,並在38.1 kW/cm2雷射光的激發強度下,發生激發輻射(stimulated emission)現象。接著利用在非晶質基板上成長ZnO薄膜的經驗,我門進一步藉由熱處理的方式在非晶質基板上製作p型ZnO薄膜,並應用於n-ZnO/i-ZnO/p-ZnO的結構,成功製作出發光波長為紫外光的ZnO均質接面發光二極體。 In this thesis, we present the fabrication and optical characteristics of the ZnO thin films and nanostructures grown by the atomic layer deposition (ALD) technique. Results indicate that ALD is a very promising technique for the preparation of high-quality ZnO for the future ultraviolet (UV) light-emitting devices. The fabrication and the characteristics of n-ZnO/p-SiC(4H) and n-ZnO/i-ZnO/p-SiC(4H) heterostructure light-emitting diodes (LEDs) were reported. Electroluminescence (EL) from the n-ZnO/p-SiC LED originated from the defect-related states in SiC due to the predominant electron injection from n-ZnO into p-SiC. On the other hand, the n-ZnO/i-ZnO/p-SiC LED exhibited dominant UV emission from ZnO. This difference is attributable to the insertion of the undoped i-ZnO layer between n-ZnO and p-SiC, leading to the injection of holes from p-SiC and electrons from n-ZnO into the i-ZnO layer to produce UV EL and the suppression of the electron injection from ZnO into SiC. The conformal step coverage of ALD was applied to deposit ZnO into the voids between the SiO2 nanoparticles. The ZnO quantum dots with diameters in the range of 3–8 nm are uniformly embedded in the SiO2 matrix. Significant blue shift in PL spectrum attributed to the quantum confinement effect of the ZnO dots was observed. We have fabricated novel UV LED structures by inserting this SiO2-ZnO nanocomposite layer between n-ZnO and p-GaN or p-AlGaN. The dominant UV EL from ZnO in the n-ZnO/SiO2-ZnO nanocomposite/p-GaN heterostructure LEDs at a low inject current was observed. The observation of amplified spontaneous emission (ASE) from ZnO in the n-ZnO/SiO2-ZnO nanocomposite/p-AlGaN heterostructure LEDs was also presented. The low refractive index of the SiO2-ZnO nanocomposite layer results in the increase in the light extraction efficiency from n-ZnO, the low-threshold optically pumped stimulated emission in n-ZnO, and the internal optical feedback of UV EL into n-ZnO layer. Significant enhancement of the UV EL intensity and super-linear increase in the EL intensity from ZnO with the injection current can be attributed to ASE in the high-quality n-ZnO layer grown by the ALD technique. An ALD process was developed to grow high-quality ZnO films on amorphous Corning 1737 glass substrates. A ZnO buffer layer was prepared on the glass substrate at a high deposition temperature of 300°C and followed by a high-temperature RTA treatment. Afterwards, highly (0001) orientated ZnO films can be grown upon the buffer layer at a low temperature of 150°C. The high optical quality of the ZnO films was demonstrated by the predominant NBE spontaneous emission at 380 nm with a negligible defect-related band and the low-threshold (38.1 kW/cm2) stimulated emission at room temperature. Finally, UV EL from ZnO homojunction LEDs grown by the ALD technique on amorphous silica substrates was presented. The p-type ZnO with hole concentration of 1.05×1017 cm−3 in the LEDs were the phosphorus-doped ZnO films fabricated by the thermal diffusion and RTA activation processes. Dominant UV EL from ZnO was achieved at room temperature in the n-ZnO/i-ZnO/p-ZnO homojunction LEDs. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/46163 |
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