Microstructure and Optical Properties of Zinc Sulfide Fabricated by Pulsed Electrochemical Deposition

硫化鋅是ㄧ個n型寬能隙直接半導體(室溫Eg=3.7eV)，非常適合應用於異質接面太陽能電池的緩衝層或是透光層。本文藉由電化學沈積法在透明導電玻璃上成長硫化鋅。在硫酸鋅和硫代硫酸鈉的電解液中，利用脈衝電化學製程(pulsed electrochemical deposition, PECD)，控制在不同電位分別做氧化或還原的反應。實驗結果發現，在陰極還原電位固定在-1.2V(vs. SCE)下，陽極氧化電位由-0.5V~-0.8V變化，氧化時間固定在4秒，可發現陽極氧化電位對鍍層表面形貌及結晶性有重大的影響。另外，陽極氧化電位-0.7V(vs. SCE)製備的鍍層較接近計量比成分。當陽極氧化時間由4秒增加為9秒時，對鍍層的表面形貌及光學性質影響不大。當電解液pH高於4時，會形成氫氧化鋅的沈積，但pH小於3時又會造成氫氣泡的形成，降低薄膜的性質，所以電解液中pH值是扮演一個很重要的角色。最後，將試片作進行300℃持溫一小時的退火處理，穿透率明顯變高，幾乎有90%穿透，但 XRD顯示出鍍層為非晶結構，從穿透圖譜看來，退火過後的鍍層很有可能為非晶結構。ZnS is an n-type semiconductor with a wide direct band gap (3.7eV at room temperature), and is potentially used as the window layer in heterojunction photovoltaic solar cell. In this present study, ZnS thin films were electroplated onto ITO from the electrolyte containing zinc sulfate (ZnSO4) and sodium thiosulphate (Na2S2O3) using pulsed electrochemical deposition (PECD), by which the potentials for oxidation and reduction reactions, respectively, were alternatively applied. Experimental results show that when the cathodic potential was set to be -1.2V (vs. SCE), the surface morphology and crystallinity of the deposit were markedly influenced by the anodic potentials that were varied between -0.5 and -0.8V while the duration was set to be 4 s. Moreover, the deposit plated at an anodic potential of -0.7V had the composition close to stoichiometry of ZnS. The surface morphology and optical properties of the deposit underwent insignificant change as the duration time of anodic half-cycle was increased from 4 to 9s. The pH of the solution also played an important role in the properties of ZnS films. That is, zinc hydroxides formed in the solution with pH exceeding 4, while extensive hydrogen evolution occurred in the solution with pH less than 3. Finally, transmittance of the deposit was increased to be around 90% after 1h of annealing at 300℃. The deposits after annealing displayed an amorphous structure as characterized by XRD. Transmission spectrum also revealed the annealed deposit can be amorphous.摘要................................ ..............I Abstract..........................................II 目次................................ .............III 圖目錄.............................. .............VIII 表目錄.............................. .............XIV 第1章 序論.........................................1 1.1 前言...........................................1 1.2 研究動機.......................................3 第2章 實驗原理及文獻探討...........................4 2.1硫化鋅介紹......................................4 2.1.1 硫化鋅材料特性..............................4 2.1.2 硫化鋅結晶結構介紹..........................5 2.2硫化鋅製備方式..................................8 2.2.1 濺鍍法......................................8 2.2.2 化學氣相沈積................................9 2.2.3 分子束磊晶.................................11 2.2.4 化學浴沈積.................................11 2.2.5 Pulsed Electrochemical Deposition(PECD)....13 2.3電化學原理.....................................14 2.3.1 電鍍.......................................15 2.3.2 電化學製程設備.............................16 2.3.3 恆電位法...................................17 2.3.4 恆電流法...................................18 2.4電化學的優勢與劣勢.............................18 2.5硫化鋅發展現況與特點...........................20 2.6硫化鋅濕式與乾式製程及結構探討.................21 2.6.1 濕式製程...................................21 2.6.2 乾式製程...................................23 2.7 硫化鋅膜厚控制及成長行為.....................24 2.8 硫化鋅穿透率與能帶探討.......................26 2.9 影響硫化鋅薄膜之因素.........................28 2.9.1 底材特性...................................28 2.9.2 試片前處理.................................29 2.9.3 電鍍溶液...................................30 2.10 未來發展與趨勢...............................31 第3章 實驗方法與步驟..............................33 3.1 試片前處理....................................33 3.2 實驗設備......................................35 3.3 溶液配置......................................36 3.4循環伏安實驗...................................36 3.5 製程參數......................................38 3.5.1 陽極氧化電壓...............................39 3.5.2 陽極氧化時間...............................39 3.5.3 電解液pH值效應.............................40 3.5.4 成長條件...................................40 3.6 熱處理........................................41 3.7薄膜分析之各類試片製作.........................41 3.7.1 鍍層成份分析試片製備.......................41 3.7.2 XRD試片製備................................41 3.7.3 穿透式電子顯微鏡試片製作...................42 3.8薄膜分析儀器...................................43 3.8.1 掃描式電子顯微鏡分析.......................43 3.8.2 穿透式電子顯微鏡分析.......................43 3.8.3 X射線繞射分析..............................44 3.8.4 電子微探測分析儀...........................44 3.8.5 UV-Visible spectrum分析....................44 3.8.6 α-step 分析................................44 第4章 實驗結果....................................46 4.1 CV關係圖......................................47 4.2 I-t關係圖.....................................49 4.3氧化總電量與還原總電量.........................54 4.4 SEM表面形貌之觀察.............................56 4.4.1 底材表面形貌...............................56 4.4.2 變動陽極氧化電壓...........................58 4.4.3 變動陽極氧化時間...........................61 4.4.4 變動pH值效應...............................64 4.4.5 熱處理.....................................67 4.5橫截面SEM觀察..................................71 4.6 XRD繞射分析...................................74 4.7電子微探測分析.................................79 4.8 α-step膜厚分析................................83 4.9橫截面TEM觀察與分析............................85 4.10材料光學性質..................................87 第5章 討論........................................95 5.1成長反應機制探討...............................96 5.2硫化鋅結構探討.................................98 5.3電源型式差別...................................99 5.4陽極氧化電壓效應...............................100 5.5陽極氧化時間效應...............................101 5.6 pH值效應......................................101 5.7陽極與陰極總電量...............................102 5.8硫化鋅薄膜結晶性...............................103 5.9缺陷與硫化鋅導電性關係.........................103 5.10硫化鋅光學特性................................104 第6章 結論........................................106 參考文獻..........................................107 附錄..............................................11