DC and RF Characterization of Tunnel Junction Light-Emitting Transistors

本篇論文的主要研究為穿隧接面發光電晶體的製程與其元件特性量測分析，我們將發光電晶體的AlGaAs/InxGa(1-x)As基-集極接面設計成高濃度的穿隧接面，同時比較銦含量分別為5 %及2.5 %的穿隧接面發光電晶體在直流及高頻特性上的差異。基-集極穿隧接面可提供額外的電洞回補到基極量子井提供額外的放光，使發光電晶體的輸出光強度和頻寬得以提升。可以藉由理論計算得知銦含量5 %的穿隧接面因為有較小的能隙而有較高的穿隧機率。此外，電晶體的基-集極接面為高摻雜濃度形成的穿隧接面，並透過直接穿隧(direct tunneling)及法蘭茲-凱爾迪西效應(Franz-Keldysh photon assisted tunneling)使得發光電晶體除了有電流調變的能力外還多了基-集極的電壓調變能力，這使得穿隧接面發光電晶體可以做為訊號混成元件。當元件操作在負微分電阻(negative differential resistance)區域時，會使光頻率響應出現鬆弛振盪造成高達12 GHz的光輸出頻寬。另外透過小訊號模型來萃取穿隧接面發光電晶體的小訊號參數，我們的到銦含量5 %的穿隧接面有較小的基-集極接面電阻驗證了5 %的穿隧接面發光電晶體有較高的穿隧機率及光輸出頻寬。 此外，我們製作出第一顆InAs/GaAs量子點發光電晶體。量子點因其特殊的量子能階及電子侷限能力在過去十年被應用在許多元件上，例如: 二極體雷射、發光二極體及光偵測器等。因此我們將量子點加入發光電晶體的基極當作主動區，並量測其輸出的電訊號及光訊號的特性曲線。This thesis presents the fabrication and characterization of tunnel junction light-emitting transistors (TJLET) with 2.5 % and 5 % indium mole fraction at the AlGaAs/InxGa(1-x)As base-collector tunnel junctions. The collector tunnel junction is an additional source of holes resupply to the base, and to recombination, providing the higher optical output and optical modulation bandwidth. The experimental data can be explained by calculating the tunneling probability. In addition, high p+ and n+ tunnel junction doping can be more effectively controlled by the change of voltage via direct tunneling and Franz-Keldysh photon-assisted tunneling, which makes possible a direct scheme of voltage modulation in addition to the usual current modulation. This is an advantage for signal processing. A resonant optical modulation bandwidth up to 12 GHz is obtained via direct voltage modulation when the TJLET is operated in negative differential resistance region. An analytical understanding of these physical characteristics is developed based on experimental data and small-signal equivalent circuit model of TJLET. From the parasitic element extraction, we find out the base-collector resistance is the key component in the operation of TJLET. Moreover, the first InAs/GaAs quantum dot light-emitting transistor (QDLET) is fabricated. The δ-function-like density of state and strong localization of electronic wave function make the QDs attractive for many device applications. In this work, the electrical and optical characteristics of QDLET are demonstrated. The emission wavelength is near ~ 1100 nm and suitable for optical communication.口試委員會審定書 # 誌謝 i 中文摘要 ii ABSTRACT iii CONTENTS iv LIST OF FIGURES vi LIST OF TABLES x Chapter 1 INTRODUCTION 1 1.1 Motivation 1 1.2 From Transistor to Light-Emitting Transistor 3 1.3 Organization of Work 6 Chapter 2 DC CHARACTERISTICS OF InGaAs TUNNEL JUNCTION ON LIGHT - EMITTING TRANSISTORS 7 2.1 Device Layer Structures and Layout Design 8 2.2 Device Fabrication 11 2.3 Operation Principle of TJLET 11 2.3.1 Characteristics of Tunnel Junction 11 2.3.2 Current Components of TJLET 13 2.4 Electrical-Optical Characteristics of TJLET 16 2.5 Direct Tunneling and Franz-Keldysh photon-assisted Tunneling 19 2.5.1 Impact of Direct Tunneling 19 2.5.2 Impact of Franz-Keldysh photon-assisted Tunneling 22 2.6 Impact of Different Tunneling Effect on the TJLET Output 25 Chapter 3 RF CHARACTERISTICS OF InGaAs TUNNEL JUNCTION ON LIGHT - EMITTING TRANSISTORS 26 3.1 Device Structures and Layout Design 26 3.2 Experimental Setup and Small-Signal Model 28 3.3 Electrical-Optical Characteristics 29 3.4 RF Characteristics 31 3.5 Small-Signal Circuit Elements Extraction 35 3.6 Parasitic Element: Rbc 39 3.7 Parasitic Effect: Rbc 42 3.8 Intrinsic Optical Response Extraction 46 Chapter 4 QUANTUM DOT LIGHT - EMITTING TRANSISTOR 48 4.1 Device Structure and Photoluminescence Spectrum 48 4.2 Device Fabrication 51 4.3 Electrical-Optical Characteristics 51 Chapter 5 CONCLUSION 54 REFERENCE 5

Magnetic Tunnel Junction with Organic Spacer

我們嘗試去組裝以有機分子或高分子為位障的磁性穿隧接面。我們用了四種方法去形成有機薄膜，其中有兩種方法成功得製備穿隧接面。此二方法是形成兩性分子的Langmuir-Blodgett (LB)膜和以旋轉塗布法製備高分子薄膜。本實驗的目標是實現在有機接面觀測到穿隧磁阻效應(TMR)，並且量測此有機磁性穿隧接面的電性、磁性、表面特性和化學性質。對於以Langmuir-Blodgett (LB)膜為位障的有機磁性穿隧接面，我們發現和磁性組態一致的穿隧磁阻效應。除此之外，我們比較了有機磁性穿隧接面在不同溫度和不同分子層下的穿隧磁阻效應。We try to fabricate magnetic tunnel junctions with the organic spacer of molecules or polymers. There are four methods we use to form organic thin layer, and two of them could successfully be used to prepare tunnel junctions. They are the method of formation of Langmuir-Blodgett (LB) films of amphibious small molecules and the method of spin coating of polymers. The main goal of the experiments is to realize the tunnel magneto-resistance (TMR) effect in the organic junction, and to measure the electric, magnetic, surface, and chemical properties of the organic magnetic tunnel junction (OMTJ). We find the tunnel magneto-resistance effect of the organic magnetic tunnel junction with the organic spacer of Langmuir-Blodgett (LB) film, which is consistent with the magnetic configuration. In addition, we compare the TMR effect at different temperature and with different molecular layers.1. Introduction and Motivation……………………………………………1 2. Apparatuses and Chemicals……………………………………………4 2.1. System of preparation 2.1.1. Sputtering system in ultrahigh vacuum 2.1.2. Preparation system of Langmuir-Blodgett films 2.1.3. Spin coating system 2.2. System of analysis 2.2.1. Electric properties 2.2.2. Magnetic properties 2.2.3. Morphology and thickness 2.2.4. Chemical properties 2.3. Chemicals and Materials A. Ferromagnetic material B. Pi-conjugated small molecules C. Semiconducting polymers D. Amphibious molecules E. Other chemicals 3. Experimental processes………………………………………………12 3.1. Preparation of ferromagnetic thin films 3.2. Preparation of organic spacer 3.2.1. Organic spacer of Langmuir-Blodgett films 3.2.2. Polymeric spacer 3.3. Analysis of samples A. Electric properties B. Magnetic properties C. Thickness D. Morphology E. Chemical properties 4. Results and Discussion………………………………………………15 4.1. Morphology of Ferromagnetic layers 4.2. Failure of the methods using electrodeposition and direct synthesis 4.3. The tunnel junctions with polymeric spacer using spin coating 4.4. The magnetic tunnel junction using LB film as spacer 4.4.1. Surface Pressure of Langmuir-Blodgett films 4.4.2. Morphology of Langmuir-Blodgett films 4.4.3. Successfully fabricating tunnel junction 4.4.4. Observation of TMR effect of 2 ML-LB MTJ 4.4.5. TMR effect of 2 ML-LB MTJ at different temperature 4.4.6. TMR effect of 1 ML-LB MTJ 4.4.7. Comparison with other report about metal-SAM-metal 4.4.8. Comparison with other report about MTJ using SAM spacer A. The spinvalve using pore-assistant SAM spacer B. The spinvalve using LB film and UV-lithography 5. Conclusion and future work…………………………………………34 5.1. Future work of MTJ with LB film spacer 5.1.1. Electric properties of tunnel junction using LB film A. Current-Voltage curve of MTJ B. Different electrodes C. Different SAM or embedded molecules 5.1.2. TMR effect of MTJ with LB film spacer A. TMR effect at different temperature and bias B. MTJ with different monolayer of LB film C. Determination of Thickness D. Component of MTJ E. Different molecular structure or Embedded-molecules 5.2. Improvement of the methods to fabricate MTJ with organic spacer A. Protecting layer or Ferrimagnetic layer B. Post-Annealing of MTJ with organic spacer 6. Reference

Study of microstructures and magnetoresistance of MgO based magnetic tunnel junctions

本研究以直流與射頻磁控濺鍍的方式在矽基板上鍍製磁性穿隧接面，利用超高真空的濺鍍機，配合電子束微影及氬離子蝕刻來製作微米尺度的自旋依賴穿隧接面。本實驗所鍍製的磁性穿隧接面是使用準自旋閥的結構，主要是利用兩層鐵磁性薄膜頑磁力不同，當施加一外加磁場時，隨著磁場的變化，形成兩鐵磁性層磁化方向平行與反平行兩種狀態，並利用此兩種狀態來得到低電阻和高電阻的差異。我們將針對MgO 薄膜成長於不同的鐵磁性層時（Co、CoFe、CoFeB、CoFeC)，探討其微結構和穿隧磁阻的變化，同時藉由改變工作壓力和熱處理溫度來探討MgO 薄膜微結構的改變。 經由穿透式電子顯微鏡的分析顯示，使用Co 或CoFe 底層將使MgO 薄膜形成奈米晶粒和非晶質混合的結構，且MgO 薄膜的成長不具特定結晶方向，呈現散亂的晶格排列方式。但是當MgO 薄膜成長於非晶質的CoFeB、CoFeC 或SiO2 底層時，MgO 薄膜在初鍍狀態即可具有(001)優選方向。從X 光繞射的分析顯示，當MgO 薄膜經過400 ℃、30 分鐘的熱處理後，其(001)織構未有顯著的提升，但有助於MgO 薄膜應力的釋放。 根據穿透式電子顯微鏡以及穿隧磁阻的研究結果顯示，當Os (2 nm)/CoFeB (6 nm)/MgO (2.5 nm)/CoFe (5 nm)/Ta (5 nm)樣品經過300 oC、30 分鐘的熱處理之後，可以得到約25 %的穿隧磁阻值且CoFeB薄膜會利用MgO 的表面形成MgO (001)[100]//CoFeB (001) [110]的磊晶關係。此外，由於CoFe 薄膜成長於MgO 表面時不具有特定的結晶方向，呈現散亂的晶格排列方式，當薄膜中局部區域有較多的MgO (001)//CoFe (001)磊晶關係存在時，將可得到較大的穿隧磁阻值（~90 %）。當我們於MgO 薄膜和CoFe 薄膜間引入CoFeB 中間層時，CoFeB/CoFe 上磁性層將於初鍍狀態形成（111）從優取向，此有助於提升初鍍薄膜的穿隧磁阻值，將會由Os (2 nm)/CoFeB (6 nm)/MgO (2.5 nm)/CoFe (5 nm)/Ta (5 nm)薄膜的1 %提高至Os (2 nm)/CoFeB (6 nm)/MgO (2.5 nm)/CoFeB (1.2 nm)/CoFe (3 nm)/Ta (5 nm)薄膜的12 %。但是當後者經過300 ℃、30 分鐘的熱處理後，仍可得到約25 %的穿隧磁阻值，即鐵磁性中間層的引入對於最佳穿隧磁阻值的提高並無顯著效果。此外，根據CoFeC/MgO/CoFe 磁性穿隧接面的研究結果顯示，當初鍍Os (2 nm)/CoFeC (6 nm)/MgO (2.5 nm)/CoFe (3 nm)/Ta(5 nm)樣品經過150 ℃的熱處理後，穿隧磁阻值可以由9 %提高至12 %，但是隨著熱處理溫度繼續提高，穿隧磁阻值和RA 值則逐漸降低。根據電流-電壓曲線的量測結果顯示Os/CoFeC/MgO/CoFe/Ta 樣品的絕緣層特性在經過350 ℃、30 分鐘熱處理後已被明顯的破壞。Magnetic tunnel junctions are deposited on Si substrate by dc and rf magnetron sputtering in an ultra-high vacuum chamber. The micro-sized spin-dependent tunnel junction is patterned by e-beam lithography and ion-milling. The pseudo-spin valve magnetic tunnel junction is fabricated in this work. Due to the difference in the coercivity between two ferromagnetic layers, the parallel and antiparallel spin states of the two ferromagnetic layers can be obtained as the magnetic field is varied. The effects of underlayer materials, working pressure and annealing temperatures on the microstructure and magnetoresistance of the MgO film are investigated. TEM analysis shows that the as-deposited MgO film with Co or CoFe underlayer has nanocrystalline structure or mixing phases of nanocrystalline and amorphous. Besides, the MgO grains are random-oriented. The as-deposited MgO thin film with (001) preferred orientation is obtained as the MgO film is deposited on CoFeB、CoFeC or SiO2 underlayer. X-ray diffraction analysis shows that the (001) preferred orientation of the MgO thin film does not enhance significantly after post-annealing at 400 ℃ for 30 minutes. However, that is beneficial for relaxing the stress in the MgO thin film. Magnetoresistance measurements indicate that the tunneling magnetoresistance ratio of about 25 % is obtained by annealing the Os (2 nm)/CoFeB (5 nm)/MgO (2.5 nm)/CoFe (5 nm)/Ta (5 nm) thin film at 300 ℃ for 30 minutes. The MgO (001)[100]//CoFeB (001) [110] orientation relationship can be obtained according to the TEM analysis. Because the CoFe grains are random-oriented as it is deposited on the MgO layer, the larger tunneling magnetoresistance ratio of about 90 % can be obtained for the magnetic tunnel junction with better epitaxial growth of (001) CoFe grains on (001) MgO grains. The as-deposited CoFe thin film with (111) preferred orientation can be obtained by inserting the CoFeB thin layer between the MgO and CoFe thin layers. Therefore, the tunnel magnetoresistance ratio for the as-deposited magnetic tunnel junction is increased from 1 % for the Os (2 nm)/CoFeB (6 nm)/MgO (2.5 nm)/CoFe (5 nm)/Ta (5 nm) thin film to 12 % for the Os (2 nm)/CoFeB (6 nm)/MgO (2.5 nm)/CoFeB (1.2 nm)/CoFe (3 nm)/Ta (5 nm). It is observed that the insertion of the ferromagnetic spacer does not improve the magnetoresistance ratio after 300 ℃ annealing. The tunnel magnetoresistance ratio for the Os (2 nm)/CoFeB (6 nm)/MgO (2.5 nm)/CoFeB (1.2 nm)/CoFe (5 nm)/Ta (5 nm) thin film is about 25 % after annealing at 300 ℃ for 30 minutes. The tunnel magnetoresistance for the as-deposited Os (2 nm)/CoFeC (6 nm)/MgO (2.5 nm)/CoFe (3 nm)/Ta (5 nm) thin film is increased from 9 % to 12 % after annealing at 150 ℃. However, the tunnel magnetoresistance and the resistance-area product are decreased as the annealing temperature is increased above 150 ℃. From the I-V curve measurement of the Os/CoFeC/MgO/CoFe/Ta thin film, it can be see that the barrier properties is deteriorated after annealing at 350 ℃ for 30 minutes.中文摘要……………………………………I 英文摘要……………………………………III 目錄………………………………………V 圖目錄……………………………………IX 第一章 前言……………………………………1 第二章 理論基礎與文獻回顧…………………3 2-1 理論基礎……………………………………3 2-1-1 各類磁阻簡介…………………………3 2-1-2 自旋相關穿隧效應……………………………7 2-1-2 磁性穿隧接面的應用………………………12 2-1-3-1 磁性隨機存取記憶體…………………………12 2-1-3-2 硬碟讀取頭……………………………………14 2-1-4 磊晶Fe/MgO/Fe 多層膜之穿隧磁阻理論………16 2-2 文獻回顧……………………………………20 第三章 實驗方法………………………………………35 3-1 實驗流程……………………………………………35 3-2 靶材選取………………………………………………36 3-2-1 磁性層靶材…………………………………36 3-2-2 Ta 及Os 靶材…………………………37 3-2-3 MgO 靶材靶材…………………………37 3-3 基板製備………………………………………37 3-3-1 基板選取……………………………37 3-3-2 基板清洗………………………………………37 3-4 實驗裝置與薄膜製備…………………………………38 3-4-1 實驗裝置………………………………………38 3-4-2 薄膜濺鍍………………………………………39 3-4-3 薄膜熱處理………………………………………39 3-5 穿隧磁阻樣品製作……………………………………40 3-5-1 Hard mask……………………………………40 3-5-2 電子束微影……………………………………40 3-6 基本性質分析與量測…………………………43 3-6-1 AFM 表面粗糙度觀察…………………43 3-6-2 薄膜磁性分析……………………………43 3-6-3 磁阻量測系統…………………………44 3-6-4 XRD 繞射分析…………………………44 3-7 薄膜組成及縱深分析………………………45 3-7-1 ESCA 表面分析…………………………45 3-7-2 EDS 成分分析………………………………45 3-7-3 AES 元素縱深分析…………………………46 3-8 薄膜微結構分析…………………………………………47 3-8-1 TEM 微結構觀察………………………………47 3-8-2 SEM微結構觀察…………………………………50 第四章 結果與討論…………………………………………61 4-1 薄膜的微結構觀察…………………………………61 4-1-1 Co/MgO/NiFe 薄膜之微結構觀察……………………61 4-1-2 CoFe/MgO/CoFeB 薄膜之微結構觀察………………69 4-1-3 CoFeB/MgO及CoFeC/MgO薄膜之微結構觀察……………70 4-1-4 CoFeB/MgO/FePt 薄膜之微結構研究…………………83 4-1-5 氬氣壓力對MgO 薄膜微結構的影響…………………86 4-2 穿隧磁阻的研究……………………………………………88 4-2-1 CoFeB/MgO/Co 磁性穿隧接面…………………89 4-2-2 CoFeB/MgO/CoFe 磁性穿隧接面…………………92 4-2-3 CoFeC/MgO/CoFe 磁性穿隧接面…………………95 4-2-4 CoFeB/MgO/CoFeB/CoFe 磁性穿隧接面…………………98 第五章 結論…………………………………………………149 參考文獻…………………………………………………153 研究著作………………………………………………………16

磁穿隧接面磁場感應器之低頻雜訊特性研究

我們研究磁穿隧接面磁場感測器的低頻雜訊的行為。磁穿隧接面（MTJ）由多層膜組成，結構為Ta X nm/Co40Fe40B20 1.2 nm/ MgO 2.0 nm/ Co20Fe60B20 2.3 nm/Ta 5 nm/ Ru 5 nm (其中X在 15至 30 nm之間)，其具有垂直的磁滯異向性。實驗中由自製電池盒提供樣品固定電流，將樣品雜訊經由低頻訊放大器(SR560)放大後，進入頻譜分析儀(SR785)進行訊號頻譜量測。量測得電壓雜訊，其量測頻段由1 Hz至10 kHz之間。對MTJ施加從0到100 nA之外加電流（I），觀測元件的雜訊變化。由量測到的頻譜觀察到低頻的1 / f雜訊隨外加電流增加而變大，在零磁場時，不同樣品的1 / f雜訊的Noise Amplitude 會隨樣品電阻變大而有變大的趨勢。於某些樣品，在無外場下，觀察到勞倫茲雜訊出現在26到36 Hz之間，且訊號隨著電流值變大而強度增大。 另外，我們利用自製外加磁場系統進行變磁場實驗，再給予固定通過樣品的電流，發現其雜訊變化的趨勢與樣品電阻隨磁場變化的趨勢有極高的一致性，可見雜訊大小隨磁場改變與電阻相對磁場的改變是有相關的。We investigated the low frequency noise behavior of magnetic tunnel junction based on out-of-plane field sensors. The magnetic tunnel junction (MTJ) multilayer consists of Ta X nm/Co40Fe40B20 1.2 nm/ MgO 2.0 nm/ Co20Fe60B20 2.3 nm/Ta 5/ Ru 5 nm (X~ 15 to 30 nm), which has orthogonal magnetic anisotropy. The voltage noise signal of the sample biased by a battery bank is fed into a low noise preamplifier (SR560) and analyzed by a dynamic signal analyzer (SR780) with the frequency range set from 1 Hz to 10 kHz. As various bias current (I) from 0 to 100 nA flows through the MTJ field sensor, we can observe that the power spectrum density (PSD) of the low-frequency 1/f excess noise increases with I and follows Hooge's fomula SV = AV2/f, where A is the noise magnitude, V is the voltage across the device, and is a constant close to 1. The noise amplitude increases as the resistance increases at zero field. We also found that the Lorentzian noise was embedded in the 1/f noise spectra of several samples between 26 Hz and 36 Hz and increased as the bias current increased. At a fixed bias current, we investigated the noise of MTJs in various magnetic fields. From the results, the trend of the PSD change of the 1/f noise in magnetic fields is similar to that of the magneto-resistance of the sample. It indicates that the variation of the noise is strongly correlated to the magneto-resistance.第一章 緒論 1.1 研究背景………………………………………………… 1 1.2 研究動機………………………………………………… 2 1.3 論文架構………………………………………………… 3 第二章 原理與物理模型 2.1 鐵磁穿隧接面介紹……………………………………… 4 2.2 雜訊介紹………………………………………………… 6 2.2.1 熱雜訊…………………………………………… 6 2.2.2 閃爍雜訊………………………………………… 7 2.2.3 勞倫茲雜訊……………………………………… 9 第三章 樣品與量測系統 3.1 MTJ樣品製程與結構…………………………………… 10 3.2 量測系統………………………………………………… 12 3.2.1 雜訊量測系統……………………………………… 12 3.2.2 變磁場系統………………………………………… 15 第四章 量測與數據分析 4.1 無外加磁場雜訊量測………………………………… 18 4.2 變磁場雜訊量測……………………………………… 24 4.3 勞倫茲雜訊分析……………………………………… 27 第五章 總結………………………………………………………… 35 參考文獻……………………………………………………………… 3

First Principles Calculations on 2D Heterojunctions and Optical Transition Mechanisms of Perovskite MAPbI3

在此研究中，吾人首先以第一原理計算探討二為材料異質接面的性質。考慮的二維材料異質接面系統有包含石墨烯及其衍生物、二硫化鉬與六方晶系之氮化硼。這些二維材料彼此之間可以水平方式或垂直方式堆疊，且皆展現了特殊的性質以及應用。吾人將探討石墨烯基底的水平接面、二硫化鉬基底的水平接面與石墨烯/氮化硼/石墨烯的垂直接面。以水平接面來說，吾人主要關注其肖特基能障，亦即其能帶排列。對於垂直接面，其主要應用於穿隧接面元件，故吾人將關注能帶排列與其在外加電場下的行為。這些接面將可應用於各類奈米電子元件。 第二部份中，吾人將探討鈣鈦礦結構之甲胺鉛碘的光學吸收機制。此材料因其在可見光區有很強的吸收，近年來被廣泛運用於太陽能電池的吸光材料且得到很高的光電轉換效率。因此，研究其光學吸收機制將有助於釐清其關鍵之處。吾人將運用「能帶解析光學吸收密度」技術探討之。We have employed the first-principle calculations to investigate the interfaces of 2D materials in the first part. The considered 2D materials are graphene and its derivatives, MoS2 and hexagonal boron nitride. These 2D materials can be stacked horizontally or vertically. Both of them show special properties and would have some special applications. We research graphene-based horizontal junctions, MoS2-based horizontal junctions and graphene/h-BN/graphene vertical junctions. For horizontal junctions, we focus on Schottky barrier heights, i.e., band alignments. For vertical ones, they can be applied as tunneling junctions; hence band alignments under electric fields are important. This junction can be potentially used in the nanoelectronics. Secondly, we investigate the optical transitions of perovskite MAPbI3. This material is widely used in the active layer of the solar cell device currently because of the strong absorption near visible-light region and the high power conversion efficiency of the device. Therefore, the optical transition near visible-light region would be the key factor. The band-resolved absorption density analysis is applied to investigate the optical transition mechanism

Tunnel Magnetoresistance Under Proximity Effect in NiFe/CoFe/Al2O3/CoFe/Nb

摘要 磁性穿隧接面由鐵磁/絕緣/鐵磁所構成，穿隧磁電阻效應的高低主要取決於「鐵磁/絕緣」介面上的磁性和電子組態。藉由引入超導層，在鐵磁/超導鄰近效應中，我們來觀察鐵磁層中電子傳輸是否受到超導層影響。經由對照組我們發現在低溫進入超導態時，反平行態電阻受到超導層鈮的影響隨著溫度降低而降低，而平行態電阻則不受超導影響，其現象就是磁電阻率的降低。 在不同厚度的鈮，我們發現鈮厚度在低於100 nm時，磁電阻率在超導態時明顯不受影響。比較鈮厚度500 nm，鈮厚度在150 nm ~250 nm時，磁電阻率在溫度降低至超導轉變溫度時會有延遲降低的現象。Abstract The magnetic tunnel junctions (MTJs) are consisted of ferromagnet/insulator/ferromagnet (FM/I/FM). Tunnel magnetoresistance (TMR) is strongly influenced by the electronic and magnetic properties at the FM/I interface. Considering the proximity effect in ferromagnet/superconductor (FM/SC), we sputtered Nb on the top FM layer of pseudo spin-valve (PSV) magnetic tunnel junctions to observe how the superconducting Nb influences the FM layer. With the help of the contrast experiment, we find that the resistance of the antiparallel state maybe influenced by Nb and it becomes lower below the superconducting transition temperature (Tc). However, the resistance in paralleled state is not significantly influenced by Nb, resulting in the decrease of TMR values. In the thickness dependence of Nb, we find that TMR is not apparently influenced in SC state as the thickness of Nb is below 100 nm. Comparing with that in the case of 500 nm Nb thickness, the TMR value shows retarding decrease as cooling through Tc for those of Nb thickness between 150 nm and 250 nm.目 錄 第一章 簡介 1 第二章 基本原理 3 2.1 磁電阻 3 2.1.1普通磁電阻 4 2.1.2異向性磁電阻 4 2.1.3龐磁阻 5 2.1.4巨磁阻 5 2.1.5穿隧磁電阻 7 2.2 超導體 11 2.2.1零電阻和邁斯納效應 11 2.2.2倫敦方程和超導穿透深度 13 2.2.3鄰近效應 16 2.3.2磁性與超導的相互影響 17 第三章 實驗技術 18 3.1 超高真空系統 18 3.1.1抽氣系統 18 3.1.2真空壓力計 21 3.2 濺鍍系統 23 3.2.1直流和交流濺鍍 23 3.2.2磁控濺鍍 25 3.3元件製程 26 3.4四點量測法 28 第四章 實驗結果與分析 29 4.1 NiFe/CoFe/Al2O3/CoFe/Nb(500nm) 31 4.2 Superconducting thickness dependence 44 4.3超導穿透深度和磁電阻率的關係 61 第五章 結論 63 第六章 參考資料 6

Magnetoimpedance Effect of Spin Dependent Tunnel Junction

量測自旋穿隧電子元件 (the spin dependent tunnel junction)的磁電阻行為通常是利用直流電源來提供電流或電壓。在本論文實驗中,磁性穿隧接面 (magnetic tunneling junction, MTJ) CoFe/Al2O3/CoFe/NiFe 使用HP4294A 提供40 Hz~110 MHz交流電流源，利用四點量測方式，在室溫下量測MTJ的磁阻抗 (magnetoresistance) 行為，我們可提供的磁場最大可達一千高斯左右。 當MTJ在交流電源中，由於MTJ結構關係由於MTJ結構關係我們將不只單單考慮穿隧電阻部分，電容所扮演的角色將會影響MTJ磁阻抗效應隨著頻率變化的關係，其中電容值得大小是與形狀和材料所決定的，但是我們發現，當外加不同磁場時，電容的大小會受到磁場而改變•另外在量測高頻阻抗行為時，我們也發現阻抗的實部大小會由正數轉電成負數，會產生此種現象是類似於因為四點量測所產生的電流分布效應，當我們MTJ的導線電阻與穿隧電阻大小相近時，電流分布效應集會產生，並有可能量到負的電阻值，然而交流電源系統中，電流分布效應的產生就必須考慮與頻率的關係。在製作MTJ絕緣層的步驟中，穿隧位障的形成是使用氧氣電漿來氧化鋁膜，我們可以控制氧化過程的時間，來製作不同大小的有效穿隧電阻，並觀察發生負實部阻抗的特徵頻率會與不同大小的穿隧電阻有何關係。也由於負的實部阻抗產生，造成我們會量到一個趨近正負無窮大的實部磁阻抗率 (TM-Re)。另外我們也觀察加上不同大小的直流偏壓與交流振幅，除了觀察磁阻抗在不同頻率中所受到的影響，並可以估計出穿隧電阻與電容受電壓增加時，分別是會下降與升高。The electronic properties of the spin dependent tunnel junction (STJ) are usually measured by direct current (DC) source. In our measurement, the MTJs CoFe/Al2O3/CoFe/NiFe was measured by a four-probe method at room temperature in the frequency range from 40 Hz to 110 MHz, with the external magnetic field ranging in strength up to 500 Oe. At high frequency, the capacitance will play an important role to affect the measured result. Generally speaking, the capacitance is determined by the geometry and materials. But We observed that the effective capacitance changes with the application of an external magnetic field. The magnetocapacitance ratio can get up to 15%. At high frequency, The real part of impedance was found to change from positive to negative. The phenomenon is similar to the inhomogeneous current distribution effect that derived from the electrode resistances comparable to or higher than the junction resistance. The MTJs with a tunnel barrier formed by O2 plasma. We control the time of O2 plasma sputerring in forming the tunnel barrier is effective for achieving a different junction resistance and for causing the oxidation degree of the bottom electrode during plasma oxidation in MTJs. By the way to caculated the critical frequency that the real part cahege sign. At this critical frequency, the real part of magetoimpedance (TM-Re) have a huge increase.第一章 簡介 1 第二章 基本原理 3 2.1 磁電阻 (magnetoresistance)……………………...…3 2.1.1 普通磁電阻 (ordinary magnetoresistance , OMR)…………4 2.1.2 異向性磁電阻 (anisotropic magnetoresistance, AMR)…...…4 2.1.3 龐磁阻 (colossal magnetoresistance , CMR). .……………6 2.1.4 巨磁阻 (gaint magnetoresistance , GMR) . .……..………7 2.2 穿隧磁阻 (tunneling magnetoresistance , TMR) ……. 9 2.2.1自旋極化穿隧 (spin-polarized tunneling) .…..…..………9 2.2.2 Jull

Amorphous and Microcrystalline Silicon Thin Film Solar Cell Simulation

本論文中，介紹了以非晶矽為主的薄膜太陽能電池。一開始先介紹了關於非晶矽的一些材料特性，以及所有在模擬中所用到的參數。然後模擬單一吸收層的非晶矽以及微晶矽，並且將結果與實驗值做比較。除此之外，針對單一吸收層的非晶矽以及微晶矽，做了對吸收層的厚度的最佳化。 接下來探討將兩層結構串在一起，也就是串疊型的太陽電池。由於兩層結構的介面需要一層”穿隧接面”來讓光電流得以在介面複合，因此在模擬中必須將此考慮進去。然後將模擬結果跟實驗值比較也得到吻合的結果。因為串疊型的太陽電池必須考慮上下兩層結構所產生的電流要盡量吻合，才能達到比較好的輸出功率。因此做了上下兩層結構的厚度最佳化模擬。 由於材料特性的關西，太陽光之中能量比較小的部份並沒有辦法被非晶矽以及微晶矽所吸收，所以探討了加上一層鍺，並且發現可以提升太陽電池的轉換效率。因為鍺材料比較昂貴，所以也模擬了鍺的厚度對於效率的影響，希望用較少量的鍺來達到提升效率的目的。最後提出了一個新的結構:p-i-i-n。模擬之後發現，此結構的效率跟串疊兩層的太陽電池差不多。由於此結構比起串疊式較為簡單，希望可以藉此減低製程困難度。In this thesis, the amorphous Si based thin-film solar cell is introduced. First, the model for single junction simulation is established. The disorder in the amorphous Si, which causes the tail states and deep states distribution, is also considered in the simulation. The single junctions of amorphous Si and microcrystalline Si are compared with the experiment data. Furthermore, the optimal thicknesses of i-layer of amorphous Si and microcrystalline Si are discussed. The simulation of double junction with two p-i-n single junctions in series is also discussed. For the current matching, the optimal thicknesses of top and bottom cells are discussed. With the addition of Germanium layer, the efficiency of triple junction solar cell could reach about 12%. Finally, the pi-i-n structure provides a new concept for fabricating solar cells.中文摘要 IV文摘要 Vist of Figures IXist of Tables XIIhapter 1 Introduction 1.1 Motivation 1.2 Organization 2eferences 2hapter 2 Simulation of Amorphous and Microcrystalline Silicon Single Junction Thin Film Solar Cells 3.1 Introduction 3.2 Physics of Solar Cells 4.2.1 The Solar Spectrum 4.2.2 Characteristics of the Solar Cell 7.3 Amorphous and Microcrystalline Silicon Single Junction p-i-n Solar Cells 8.3.1 P-i-n Structure and Parameters of Amorphous Silicon 9.3.2 P-i-n Structure and Parameters of Microcrystalline Silicon 12.4 Comparison of ISE Simulation and Experiment 14.5 Optimal Thickness of i-layer in the Amorphous Silicon p-i-n Single Junction Solar Cell 17.6 Optimal Thickness of i-layer in the Microcrystalline Silicon p-i-n Single Junction Solar Cell 19.7 Summary 21eferences 22hapter 3 Amorphous Silicon / Microcrystalline Silicon Tandem Solar Cell Simulation 24.1 Introduction 24.2 The Basic Structure of Amorphous Silicon / Microcrystalline Silicon (micromorph) Tandem Cell 25.3 Comparison of the ISE simulation and Experiment 29.4 Optimal Thickness of i-layer in Tandem Cell for Current Matching 30.5 Summary 36eferences 37 hapter 4 Device Improvement 38.1 Introduction 38.2 The Tunnel Junction 39.3 a-Si:H/uc-Si/Ge Triple Junction Solar Cell 42.4 The p-i-i-n Structure Solar Cells 48.5 Summary 52eferences 53hapter 5 Summary and Future Work 55.1 Summary 55.2 Future Work 5

Characterization of Heterojunction Bipolar Phototransistor with Integrated Two-Section Light-Emitting Transistors and Logic Gate Application

在資訊爆炸的時代，將光訊號與電訊號整合於同一晶片上形成光電積體整合電路(OEICs, OptoElectronic Integrated Circuits)是未來重要的研究發展之一。發光電晶體(Light-Emitting Transistor, LET)有著獨特的電訊號輸入、光訊號與電訊號同時輸出的雙輸出的特性，且具有快速的載子複合速度。此外，發光電晶體與傳統光電晶體(Heterojunction phototransistor, HPT)磊晶結構相仿，同樣都在基極、集極與次集極間形成p-i-n二極體的光吸收層，因此可將發光電晶體作為光電晶體來當作光偵測器使用。由上述可知，發光電晶體集合了光源與接收端的特性，使之成為下一世代光電積體整合電路重要的發展元件之一。 本研究將兩顆發光電晶體整合於同一元件上，形成一個兩段式整合元件，其中一者為光訊號輸出端，另一者為光訊號之接收端。同時操作下，分析其作為光接收端的元件，在外部光注入下其直流電訊號與高頻特性的改變。隨著操作偏壓、工作電流以及光注入的改變，光電晶體的光響應度可達711.4 A/W。我們另外將穿隧接面引入元件的結構中，發現若有額外的穿隧電流的影響，則穿隧式光電晶體的光響應度可達3404.8 A/W。在元件的高頻特性部分，在有光訊號注入之後，光電晶體的截止頻率由1.4 GHz推至1.51 GHz，我們利用等效小訊號模型分析元件受到電容電阻寄生效應的影響。最後我們利用發光電晶體設計一個以光訊號為主的邏輯電路，形成AND閘與OR閘，並可以得到顯著的光訊號邏輯變換特性。 為了增進元件特性表徵，未來可以以「電晶體雷射」取代發光電晶體，以及設計波導結構來提升元件光訊號輸出與準直性，並可設計NAND閘與NOR閘，使光電邏輯電路運用廣泛。In an era of information explosion, combining optical and electrical signals into a single chip to form OptoElectronic Integrated Circuits (OEICs) is one of the most important researches and developments in the future. In 2004, Milton Feng and Nick Holonyak, Jr. invented the first light-emitting transistor (LET) in UIUC. The III-V LETs with a direct bandgap and carrier injection have made themselves as three-port (an electrical input, an electrical output and a “third-port” optical output) devices. The LETs has a similar epitaxial structure to the conventional heterojunction bipolar transistor (HBT). The base, collector and subcollector layer of the LET can be employed to form a p-i-n diode for photon detection, which works as a heterojunction phototransistor (HPT). Therefore, the LET has the unique characteristics to function like a photon transmitter and receiver, which has the potential to become a building block for next-generation OEICs. In this thesis, we demonstrate an integrated two-section light-emitting transistor with one section working as a light emitter and the other one working as a phototransistor. Firstly, we use this two-section device to characterize the HPT with different operation points (IB and VCE) and injected optical power. The responsivity of the HPT is 711.4 A/W. A tunnel junction is then incorporated to form a tunnel junction heterojunction phototransistor (TJ-HPT). With the help of the tunnel junction, the responsivity can be enhanced to 3404.8 A/W. Secondly, we characterize the microwave performance of the LET under different optical injections. Through the analysis of small-signal equivalent circuit models, we can analyze the transist time by deembedding the circuit paracistics effect. The cut-off frequency enhances from 1.4 GHz to 1.51 GHz under an optical power injection. Thirdly, we design and demonstrate the optical logic gates in the form of an AND gate and OR gate utilizing the characteristics of phototransistors. The AND gate and OR gate have a significant on/off ratio with injecting optical power. In the future, we can enhance the performance of the two-section device by substituting theLET with the transistor laser (TL). Also we can design an optical NAND gate and NOR gate for future application of OEIC design

Fabrication and Characteristics of Superconducting/ Magnetoresistive mixed sensors

本篇論文研究超導/磁阻混合感測元件，主要結構為釔鋇銅氧(YBCO)/二氧化鈰(CeO2)/鑭鈣錳氧(LCMO)，我們利用脈衝雷射蒸鍍在鈦酸鍶(SrTiO3)基板上沉積鑭鈣錳氧鐵磁性薄膜，經過黃光微影與離子蝕刻後，再以脈衝雷射蒸鍍成長二氧化鈰以及釔鋇銅氧高溫超導薄膜，藉由絕緣層來隔絕上下的超導層與鐵磁層。利用X-光繞射儀與原子力顯微鏡來分析薄膜的特性、四點量測和磁性量測系統對元件進行電性與磁性的探討。 我們設計兩種不同磁阻類型的元件，一是以鑭鈣錳氧薄膜為主，另一是製作階梯式穿隧磁阻元件(TMR)，利用離子蝕刻在基板上蝕刻出階梯。測量製作出來的鑭鈣錳氧相轉變溫度為256 K以及釔鋇銅氧有良好的臨界溫度，並量測元件的特性。我們比較有超導環以及沒有超導環的樣品，發現沒有超導環在230 K的環境下其穿隧磁阻最大值達37 %。In the thesis, we have studied the superconducting / magnetoresistive mixed sensors, which structure is YBCO/CeO2/ LCMO. The LCMO layers are grown on STO substrates by using plused layser deposition (PLD). Then we define the pattern by photo lithography and ion-milling. CeO2 and YBCO films are grown by PLD. The CeO2 layer is to avoid short between superconducting and ferromagnetism layer. The crystalline orientation and surface morphology are characterized by X-ray diffraction and atomic force microscope (AFM). The electric and magnetic properties are also studied by using four-point probe and magnetic property measurement system. We design two different type of magnetoresistance device. One is based on LCMO thin films, the other is tunneling magnetoresistance (TMR) junctions with artificial step-edge grain boundaries by using ion-milling. The metal-insulator transition temperature of LCMO is 256 K and superconducting YBCO films reveal a high transition TC. By measuring the characteristics of the divice, we find the maximum TMRmax is 37 %, which is non-YBCO loops in 230 K.目錄 口試委員會審定書 誌謝……………………………………….…………………………………….…..…...i 中文摘要…………………………………………………………………………...........ii Abstract…………………………………………………………………………………iii 目錄……………………………………………………………………………………..iv 圖目錄………………………………………………………………………………….vii 表目錄………………………………………………………………...............................x Chapter 1 緒論………………………………...…………………………………….......1 1.1 前言………………………………………..………………………………….1 1.2 磁阻介紹之發展與應用…………………………………..………………......2 1.3 研究動機…………………….………………..………...…………………......6 Chapter 2 理論介紹...……...……...…......……………………………………………7 2.1 磁性理論……………….………………..………...………………………......7 2.1.1 磁性歷史……….………………..………...………………….………..7 2.1.2 磁性原理……….………………..………...………………….………..7 2.1.3 磁性種類…….………………..………...………………….……..........8 2.2 磁阻效應(magnetoresistance)……….….………...……………………….…11 2.2.1 磁阻原理…………….……………..………...…………………….....11 2.2.2 異向性磁阻……….………………..………...………………….........12 2.2.3 龐磁阻….………………..………...…………………………...…......13 2.2.4 穿隧磁阻.………………..………...…………………………...…......13 2.3 超導理論………………………………………………………………..........15 2.3.1 超導發展歷史…………..………...…………………………...….......15 2.3.2 超導體特性………..………...………………………………...……...16 2.3.3 超導體分類………..………...………………………………...….......17 2.4 混合感測元件(the mixed sensor)………………………………………..…..18 2.4.1 元件模型…………...……………………...……………………....….18 2.4.2 磁阻元件……………………………………………………………...19 2.4.3 超導線圈磁通轉換器(flux-to-field transfomer) …………………......21 2.4.4 雜訊種類…………………....................................................................23 2.4.5現況與問題………………….................................................................24 Chapter 3 實驗方法與儀器…………………………………...…………..…………..25 3.1 實驗流程……………….……………..…………..……………………….....25 3.2 基板清洗與選擇………..……….……………………………………….......26 3.3 脈衝雷射蒸鍍(pulsed laser deposition) …………………………..…............26 3.3.1 脈衝雷射原理………..……….…………………..……......……........26 3.3.2 薄膜製程…………………….…………………..………………........27 3.4 濺鍍法(sputtering)…….………………………..…………….…...................28 3.5 微影製程(photo lithography) .…………….…..…………….….....................29 3.5.1 黃光無塵室…………….......................................................................29 3.5.2 微影步驟…………….…..…………….…...........................................30 3.6 蝕刻(etching)…………………………………………………………………33 3.6.1 蝕刻原理……………………………………………………………...33 3.6.2 離子蝕刻(ion-milling)………………………………………………...34 3.7 量測系統………………………………………………..................................34 3.7.1 四點量測…………………………………………………………..….34 3.7.2 X-光繞射……………………………..………...................................36 3.7.3 原子力顯微鏡(AFM).………………………………...........................37 3.7.4 磁性量測系統(MPMS) .……………………………….......................38 Chapter 4 實驗結果與討論 .……………………………….........................................40 4.1 薄膜特性與分析.……………………………….............................................40 4.1.1 XRD分析.………………………………..............................................42 4.1.2 電性分析.………………………………..............................................43 4.1.3 AFM分析………………………………...............................................45 4.2 超導/磁阻感測元件……………………….....................................................46 4.2.1 元件結構……………………………………………………………...46 4.2.2 光罩設計……………………………………………………………...47 4.2.3 結果分析...……………………………….…………………………...50 Chapter5 結論……………………………………………………………………….…64 Reference…………………………………………………………………………….....65 圖目錄 圖1.1 鐵、鉻「超晶格」在4.2 K溫度下所呈現的「巨磁阻效應」曲線圖…...................3 圖1.2 La1-xCaxMnO3 鈣鈦礦ABO3結構圖…................................................................3 圖1.3 TMR鐵磁層/絕緣層/鐵磁層 結構圖….............................................................4 圖1.4 不同類型之人工晶界示意圖....................................................................................4 圖1.5 溫度100 K時，不同階梯角度於磁場下的磁阻變化比較....................................5 圖1.6 溫度100 K時，不同d / H於磁場下的磁阻變化比較...........................................5 圖2.1 磁性物質之磁區示意圖............................................................................................9 圖2.2 鐵磁性物質之磁滯曲線圖.......................................................................10 圖2.3 異向性磁阻之電流平行外加磁場與垂直磁場示意圖...............................12 圖2.4 龐磁阻材料之雙交換機制.....................................................................13 圖2.5 外加磁場下，造成穿隧磁阻平行態與反平行態...............................................14 圖2.6 超導體在超導態時具有的反磁性(Meissner effect) ...........................................16 圖2.7 A為混合感測元件之結構圖，B元件局部放大圖，C為超導電流造成感應磁場，影響磁性層的磁矩方向....................................................................18 圖2.8 混合感測元件之超導線圈，當z軸外加一磁場時，根據麥斯納效應，由於超導線圈的反磁性會產生感應電流，又會導致感應磁場...........................19 圖2.9 巨磁阻元件之電阻-外加磁場關係圖.......................................................20 圖2.10 穿隧磁阻元件之穿隧磁阻-外加磁場關係圖............................................21 圖2.11 混合元件之磁阻變化-外加磁場關係圖...................................................22 圖3.1 實驗流程圖....................................................................................................25 圖3.2 準分子雷射系統...............................................................................................28 圖3.3 濺鍍系統示意圖.................................................................................................29 圖3.4 微影製程步驟.....................................................................................................30 圖3.5 正光阻與負光阻之示意圖.................................................................................32 圖3.6 濕蝕刻與乾蝕刻後之形貌圖.............................................................................34 圖3.7 四點量測之示意圖.............................................................................................35 圖3.8 X-ray入射於晶體結構，因光程差產生布拉格繞射.........................................37 圖3.9 MPMS系統..........................................................................................................39 圖4.1 STO基板成長LCMO..........................................................................................40 圖4.2 LSMO/STO、CeO2/ STO、CeO2/LSMO 晶格結構圖.........................................41 圖4.3 LCMO(150nm)/STO XRD圖..............................................................................42 圖4.4 CeO2(15nm)/LCMO(150nm)/STO XRD圖........................................................43 圖4.5 不同厚度下的La0.67Ca0.33MnO3薄膜之電阻-溫度關係圖..............................44 圖4.6 La0.65Ca0.35MnO3薄膜之電阻率隨溫度變化圖..................................................44 圖4.7 LCMO(100nm)/STO之AFM..............................................................................45 圖4.8 CeO2(15nm)/LCMO(100nm)/STO之AFM.........................................................45 圖4.9 左為LCMO圖形蝕刻後示意圖，右為圖形局部放大圖..................................46 圖4.10 LCMO圖形蝕刻後示意圖................................................................................47 圖4.11 元件結構示意圖...............................................................................................47 圖4.12 鐵磁層設計圖，右上為微橋放大圖.................................................................48 圖4.13 綠色部分為超導層設計圖，右圖為局部放大圖.............................................48 圖4.14 階梯式光罩圖...................................................................................................49 圖4.15 TMR鐵磁層設計圖，右為串聯之穿隧接面放大圖.........................................49 圖4.16 綠色部分為TMR式超導層設計圖，右為超導跨過穿隧接面放大圖...........50 圖4.17 樣品3之電阻-溫度關係圖..............................................................................51 圖4.18 樣品3之XRD圖..............................................................................................52 圖4.19 樣品1、2、4之XRD...........................................................................................52 圖4.20 LCMO電性比較圖............................................................................................53 圖4.21 光罩改設計圖...................................................................................................53 圖4.22 ion milling 示意圖............................................................................................54 圖4.23 ion milling 示意圖............................................................................................54 圖4.24 階梯AFM掃描3D圖.......................................................................................55 圖4.25 階梯角示意圖...................................................................................................55 圖4.26 階梯改善後之AFM..........................................................................................56 圖4.27 元件的電阻-溫度關係圖.................................................................................56 圖4.28 兩樣品在不同溫度下的穿隧磁阻-外加磁場關係圖.....................................57 圖4.29 穿隧磁阻-外加磁場關係圖200 K(-1000 Oe至1000 Oe) ............................58 圖4.30兩樣品在不同溫度下的磁阻-外加磁場關係圖..............................................59 圖4.31 磁阻-磁場關係圖.............................................................................................60 圖4.32 元件的電阻-溫度關係圖.................................................................................61 圖4.33 兩樣品在不同溫度下的磁阻-外加磁場關係圖.............................................62 圖4.34 (左)穿隧磁阻極大值-溫度關係圖，(右)自旋極化率-溫度關係圖..............62 表目錄 表2.1 不同磁阻之比較.................................................................................................12 表4.1 LCMO成長條件................................................................................................40 表4.2 CeO2成長條件...................................................................................................41 表4.3 不同樣品之製程條件.........................................................................................5