臺灣博碩士論文加值系統

兩點量測之氧化鋅奈米元件的電性至今已被廣泛地研究，但由於接觸面積的縮小增強了接點對奈米元件的影響，也因此在氧化鋅奈米元件中，接點的電性應該加以考慮及深入探討，才可使得兩點量測之氧化鋅奈米元件的電性傳輸更加清楚及透徹。本實驗利用電子束微影的方式，將直徑為40奈米之圓柱型氧化鋅奈米線，製成多組兩點量測之單根氧化鋅奈米線元件，量測其變溫之電流-電壓特性並分析實驗結果，發現可將元件依其室溫電阻大小分成兩類。
第一類型的元件，其室溫電阻值皆大於1 MΩ，而元件之電性深受奈米接點的影響。此類型元件之電流-電壓曲線呈現非線性及非完美對稱之特性，而電性符合熱離子發射及蕭特基效應，因此推測元件之奈米接點由蕭特基接點構成，且主導了元件的電性行為，故整體元件可用背對背之蕭特基二極體的等效電路來表示，而元件隨著溫度下降之電阻行為，在低溫下與變程式跳躍傳輸相符，推論其原因在於氧化鋅奈米線和鈦電極間可能存在非晶或無序的奈米接點；第二類型的元件，其室溫電阻約略為15 kΩ，而元件的電性呈現本質氧化鋅奈米線之特徵。此類型之電流-電壓曲線在小偏壓下呈線性行為，而電阻隨著溫度變化的行為與熱活化傳輸相符，因此推論奈米接點由歐姆接點構成，整體元件可用一歐姆電阻之等效電路加以表示。

Electrical properties of two-probe ZnO nanowire devices have been studied recently. Since the reduced contact area could magnify electrical contributions, the electrical properties at the nanocontacts of the nanowire devices should be investigated thoroughly. In this work, we adopted standard e-beam lithography and used 40-nm diameter ZnO nanowires to fabricate two-contact devices. Current-voltage (I-V) behaviors of these nanowire devices were obtained at various temperatures. We found that the devices could be categorized into two types according to their room-temperature resistances.

For type I devices, they have a room-temperature resistance much larger than 1 MΩ and display electrical properties at the nanocontacts. The I-V curves show nonlinear and asymmetric features, and they can be fitted with thermionic-emission theory implying Schottky contact effects. The devices could be modeled as two back-to-back connected Schottky nanocontacts. In addition, we found that temperature dependent resistances could be fitted well with the variable-range hopping theory so we proposed disorder and noncrystalline nanocontact model between the Ti electrode and the ZnO nanowire to explain our data. For type II devices, they usually have a low resistance at room temperature and they could exhibit intrinsic electrical properties of the ZnO nanowires. The I-V curves reveal a linear manner in low voltage. The temperature dependent resistances of the type II devices show thermal activated transport in ZnO nanowires. We argued that the type II devices could be modeled as a single ZnO nanowire with two Ohmic contacts connecting to electrodes.

中文摘要 I
英文摘要 II
致謝 III
目錄 IV
圖目錄 VI

第一章 緒論 1
參考文獻 2
第二章 文獻回顧 4
2.1 氧化鋅基本特性及其應用 4
2.1.1氧化鋅(ZnO)基本特性 4
2.1.2氧化鋅之應用 5
2.2氧化鋅奈米元件在電性上的研究 7
2.2.1 熱活化傳輸(thermal activation transport)之現象 7
2.2.2 蕭特基二極體(Schottky diode) 8
2.2.3 電子之變程式跳躍傳輸(variable-range-hopping, VRH) 10
參考文獻 12
第三章 實驗理論 14
3.1 金屬-半導體接面 14
3.1.1 蕭特基接觸(Schottky contact) 16
3.1.2 歐姆接觸(Ohmic contact) 21
3.2 熱活化傳輸(thermally activated transport) 24
3.3 變程式跳躍傳輸(Variable Range Hopping, VRH) 25
3.3.1侷域態(localized state)之概念 26
3.3.2變程式跳躍傳輸 27
參考文獻 28
第四章 實驗 30
4.1 實驗儀器與技術 30
4.1.1 高溫加熱爐 30
4.1.2 掃描式電子顯微鏡(scanning electrons microscope, SEM) 31
4.1.3 電子束微影技術(electron-beam lithography, EBL) 32
4.1.4 熱蒸鍍機(thermal evaporator) 34
4.1.5 低溫致冷器(cryostat) 36
4.2 實驗步驟 37
4.2.1 圓柱型氧化鋅奈米線之製備 37
4.2.2 單根氧化鋅奈米線元件之製備及量測 39
參考文獻 43
第五章 結果與討論 44
5.1氧化鋅奈米線及單根氧化鋅奈米線元件之觀察 44
5.2 奈米接點對奈米元件的重要性 46
5.3 奈米接點對氧化鋅奈米線元件之影響 47
5.3.1氧化鋅奈米線元件之奈米接點電性 47
5.3.2氧化鋅奈米線元件之本質奈米線電性 59
參考文獻 63
第六章 結論 64

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