以氧化鋅次微米柱製成氧化鋅薄膜及提昇氧化鋅薄膜導電度之研究

Fabrication of ZnO thin films composed of ZnO sub-microrods and improving their electrical properties

吳紋浩(Wen-Hau Wu)

指導教授 ： 林清富

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.02516

摘要

本論文的研究主要在於使用以水熱法長成的氧化鋅奈米柱製作以奈米柱構成的氧化鋅薄膜並探討如何提升其導電能力。在論文之中，我們先介紹如何以溶膠-凝膠法製作氧化鋅薄膜做為種子層、以及用水熱法成長氧化鋅奈米柱。接著我們探討以退火、氬電漿處理、準分子雷射照射以及重複生長法將氧化鋅奈米柱轉換成氧化鋅薄膜，以及上述製程對於氧化鋅奈米柱構成的氧化鋅薄膜構成的導電度的影響。在最後，我們討論以溶膠-凝膠法製作氧化鋅薄膜和使用熱蒸鍍機蒸鍍銀製作氧化鋅/銀/氧化鋅的多層結構以及提升其導電度的方法。
我們以掃描式電子顯微鏡和原子力顯微鏡觀察氧化鋅薄膜和氧化鋅奈米柱構成薄膜在經由退火製程和氬電漿處理後的表面形態，以四點探針測量樣品的片電阻，以X光繞射儀量測樣品的結晶形態，並且以紫外光╱可見光光譜儀分析氧化鋅薄膜的光學性質。氧化鋅種子層在以溫度700℃到900℃熱退火或以準分子雷射照射都會使水熱法製成的氧化鋅奈米柱的直徑變大並影響其製成薄膜的導電度。對氧化鋅奈米柱做氬電漿和熱退火處理也可提升其薄膜的導電度。XRD圖形顯示氧化鋅奈米柱構成的薄膜都具有一致沿(002)平面的方向性。以適當的時間對氧化鋅奈米柱進行氬電漿處理會改變其表面形態，並使奈米柱之間產生連結增加薄膜的導電度。然而，氬電漿處理時間過長時會蝕刻氧化鋅薄膜使氧化鋅薄膜厚度減少造成片電阻上升。結合上述熱退火和氬電漿處理可使氧化鋅薄膜的片電阻由1.2×106Ω/square降至最低293.3Ω/square，且電阻率最低可達到1.17×10-2Ωcm。
我們也使用準分子雷射照射以及重複生長的方式在低溫(200℃以下)的環境下製作氧化鋅奈米柱構成薄膜。在使用準分子雷射照射法時我們調整準分子雷射的能量密度與照射次數使奈米柱產生連結並使氧化鋅薄膜的片電阻降至1.489×105 Ω/square，由XRD圖的觀察則能發現經準分子雷射照射的氧化鋅奈米柱構成的薄膜依然保有一致的(002)平面生長方向的繞射強度。我們也結合以氬電漿處理先讓奈米柱連結在一起，並使用高能量密度準分子雷射照射替代高溫退火，可使片電阻降為4.48×103Ω/square大幅度提升以低溫製程得到以氧化鋅奈米柱構成的薄膜的導電度。另一方面，我們發現以不同大小的氧化鋅奈米柱做基底會影響重複生長奈米柱的型態，其中以較大的氧化鋅奈米柱做為基底可使重複生長的奈米柱的直徑變大且排列十分緊密。由XRD圖可得重複生長與再次重複生長的奈米柱都有非常一致的沿(002)平面方向的繞射強度且重複生長的氧化鋅奈米柱結晶品質優於直接成長的奈米柱。經一次重複生長的奈米柱可使氧化鋅奈米柱構成薄膜的片電阻降為2.271×104Ω/square。而在以氬電漿處理後因氬電漿製程提供能量給氧化鋅粒子進行再結晶，加強氧化鋅奈米柱之間的連結可使片電阻再下降至1.312×104 Ω/square。
最後，為了在提升上述以奈米柱構成單層氧化鋅薄膜的導電度，我們以溶膠-凝膠法製作氧化鋅薄膜和使用熱蒸鍍機蒸鍍銀製作氧化鋅/銀/氧化鋅的多層結構。其中，銀金屬層的厚度對氧化鋅/銀/氧化鋅結構的透光度和導電度有顯著的影響。由於氧化鋅種子層的導電度極低以及銀金屬層的銀顆粒的連結程度不高，使得我們製作的氧化鋅/銀/氧化鋅的多層結構的片電阻很高。在以600℃退火後我們的氧化鋅/銀/氧化鋅的多層結構片電阻可大幅度下降至至19.8Ω/square為本論文得到最低的片電阻，且具有良好的透光度。

關鍵字

氧化鋅 ； 奈米柱 ； 水熱法 ； 準分子雷射 ； 氬電漿 ； 片電阻

並列摘要

In our study, we report the fabrication of ZnO thin films composed of ZnO nanorods prepared by the hydrothermal method and the improving of the electrical properties. Firstly, we fabricated the ZnO thin films as seedlayers and ZnO nanorods by using the sol-gel technique and the hydrothermal method separately. Then, we discuss the methods of transferring ZnO nanorods to ZnO thin films composed of nanorods by thermal annealing, argon plasma treatments, excimer laser irradiation, and re-growing. We also study the effects of treatments mentioned above to the ZnO nanorod-composed thin films. Finaly,we fabricated the ZnO/Ag/ZnO multilayer structure with the ZnO layer made by the sol-gel process and the ultra thin silver layer evaporated by a thermal evaporator and introduced the methods to improve the conductivity of this structure.
We investigated the surface morphology of thermally annealed and argon plasma treated ZnO seedlyer and ZnO nanorods by scanning electron microscope (SEM) and atomic force microscope (AFM), measured sheet resistances of the samples by a four point probe technique, revealed the crystalline properties by X-ray diffraction (XRD) and the optical transmittance by a UV-Visible spectrometer. The diameter of grown ZnO nanorods was enlarged by conducting thermal or excimer laser annealing to ZnO seedlayers which affected the conductivity of the ZnO thin films made by those nanorods. Ar plasma treatment and thermal annealing could increase the conductivity of the ZnO thin films by connecting the nanorods and improving the crystalline properties.The ZnO nanorods with thermal annealing at different temperature or excimer laser annealing on the seedlayers are all wurtzite crystal structure and have (002) preferred orientation. The lowest resistivity of 1.17×10-2Ωcm and sheet resistance of 293.3Ω/sq was obtained from the ZnO nanord composed thin films with seedlayer annealed at 900℃ and nanorods treated by thermal annealing and argon plasma treatments.
We also utiltized the excimer laser irradiation to ZnO nanorods and re-growing method to fabricated ZnO nanorods composed thin films at low temperture environment. We adjusted the energy density of excimer laser and irradiation times to connect the nanorods and the sheet resistance was reduced to the value of 1.489×105 Ω/square. The XRD patterns revealed that the highly (002) preferred orientation of excimer laser irradiated ZnO nanorods was preserved. In order to aviod excess excimer laser irradiation destroying the nanorods, we treated the nanorods by argon plasma to connect them first then irradiated by excimer laser. The sheet resitance of samples combined of argon plsama treatment and laser irradiation reduced to 4.48×103Ω/square which is the lowest sheet resistance of ZnO thin films fabricated by low temperature process. On the other hand, we observed that the rod size and desity of re-grown ZnO nanorods could be affected by the rod sizes of base ZnO nanorods and a more large rod size and densely connected morphology of re-grown nanorods grown on the larger base ZnO nanorods would reduce the sheet resistance to the value of 2.271×104 Ω/square. The large sized and compact re-grown nanorods treated by argon plsama showed re-crystallizing at the boundaries of nanorods therefore improved the conductivity and the the sheet resistance reduced to the value of 1.312×104 Ω/square.
In order to supass the conductivity of ZnO nanorod composed thin film with various treatments metioned aboved. We introduced the ZnO/Ag/ZnO multilayer structure with the ZnO layer made by the sol-gel process and the ultra thin silver layer evaporated by a thermal evaporer. The thickness of silver layer on the ZnO/Ag/ZnO structures has a significant impact to light transmission and conductivity. Because of the high resistivity of sol-gel processed ZnO seedlayer and the discontinuity of evaporated silver layer, our ZnO/Ag/ZnO multilayer exhibted high resistivity. But after thermal annealing, the sheet resistance of ZnO/Ag/ZnO multilayer reduced dramaticly to the value of 19.8 Ω/square which was the lowest value through our study and showed good optical transparency over the entire visible lightwavelength range.

並列關鍵字

ZnO ； nanorods ； hydrothermal method ； excimer laser ； argon plasma ； sheet resistance

參考文獻

[3] 謝才淵，”利用退火及電漿製程以提昇氧化鋅薄膜導電度之研究”2008台大光電工程學研究所碩士論文

[7] 謝才淵，”利用退火及電漿製程以提昇氧化鋅薄膜導電度之研究”2008台大光電工程學研究所碩士論文

[4] 謝才淵，”利用退火及電漿製程以提昇氧化鋅薄膜導電度之研究”2008台大光電工程學研究所碩士論文

[4] 趙家忻， 2010台大光電工程學研究所博士論文

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