本論文主要探討氮化鎵奈米材料的電性及光性，可分為三部份，第一部份研究單晶結構之氮化鎵奈米線之變溫電性，第二部份探討具結構缺陷的氮化鎵奈米線之光電性質，最後一部份討論雙晶纖鋅礦氮化鎵奈米錐之光性。
第一部分研究主要是量測單晶氮化鎵奈米線的電性，了解其電性上的傳輸機制。以鎳金屬顆粒作為催化劑，利用化學氣相沉積方式製作的氮化鎵奈米線，直徑僅10~50奈米，TEM分析中可觀察到其具六方晶的單晶結構，吾人以聚焦離子束系統製做微電極後，利用客製的電性量測系統搭配低溫系統（closed-cycle cooling systems）作變溫的電性量測。在電阻與溫度的關係圖中，吾人可以觀察到在單晶氮化鎵奈米線中電子以熱活化方式及鄰近跳躍方式做傳輸，其中熱活化能約8.42 meV，極可能為表面傳導通道，而鄰近跳躍的能量約39.93 meV。
第二部份是利用導電式原子力顯微鏡探討缺陷型氮化鎵奈米線之光電性質，並以穿透式電子顯微鏡(TEM)討論奈米線之微結構。同時利用陰極螢光光譜儀（CL）進行光學性質的分析。電性的量測上，在正偏壓的部份觀察到兩處負電阻現象的產生。此外，氮化鎵為常見的寬能隙材料，且常用於金屬-半導體-金屬這類型的光偵測器，故吾人嘗試以鎢絲燈照射氮化鎵奈米線並量測其電流-電壓曲線;實驗發現，具結構缺陷的氮化鎵奈米線能產生比暗電流大八倍的次能隙光電流（sub-band-gap photocurrent）。透過TEM的分析，可以清楚地觀察到氮化鎵奈米線的中心軸部分屬於立方晶體結構（cubic），而外圍部份則是由六方晶體結構（hexagonal）所構成，此相轉換被認為是原子推疊順序的改變造成的，且依繞射圖形判斷，奈米線由雙晶結構的立方晶體結構（twinned cubic）及六方晶體結構所構成，立方晶體中的[111]方向與六方晶體中的[0001]方向相互平行;此外，在外圍的六方晶體中也觀察到存在許多的差排（dislocation），差排缺陷被認為是載子的捕捉中心（trap center），可捕捉與鎵空缺（VGa）相關的缺陷複合物（defect complex），吾人推論這些結構上的缺陷在氮化鎵的能隙中產生額外的電子能階，是造成具結構缺陷的氮化鎵奈米線元件出現負電阻及次能隙光電流的原因。此外，吾人利用CL進行此氮化鎵奈米線的光學性質分析，光譜中波峰之波長所對應的能量佐證了在微結構分析中所觀察到的缺陷型態。
最後一部分吾人研究以化學氣相沉積方式所成長之氮化鎵奈米錐結構，利用TEM及選區電子束繞射圖形(SAED)，吾人觀察到氮化鎵奈米錐呈現少見的纖鋅礦類雙晶結構，雙晶夾角（twin angle）大約118.7°，兩個(0001)面大致上以[01-11]軸做鏡射。相較於氮化鎵薄膜，氮化鎵奈米錐的拉曼光譜中可以發現兩個額外的振盪頻率，分別是420 cm^-1及709.8 cm^-1，前者為為空缺類型的點缺陷所導致的侷域振動模式（LVM），而後者是因結構表面積與體積的比值增加而產生的表面光頻（SO）模式。且奈米錐E2 (high)的峰值相較薄膜試片藍移了大約0.3 cm^-1，證實奈米錐試片相較於薄膜存在壓應力。PL光譜方面，氮化鎵薄膜與奈米錐在室溫下以near-band emission (NBE)的發光為主，且遵守Varshni effect，而後者的峰值能量稍高，應是奈米錐的成長承受著壓應力，符合拉曼光譜中的結果。此外，在低溫時，PL的量測觀察到兩個特別的峰值，能量約3.230及3.218eV，這兩峰值不隨溫度降低而改變，為束縛在結構缺陷上的激子所貢獻。

This dissertation explores the microstructures, electrical and optical properties of the GaN nano-materials. The surface morphologies of the samples were analyzed by scanning electron microscopy（SEM）. The microstructures of the sample were characterized by the transmission electron microscopy（TEM）to identify the crystalline phases. Cathodoluminescence（CL）was used to investigate the optical properties of the samples. The electrical properties of GaN nanowire were measured by conductive atomic force microscopy（C-AFM）and a home-made electrical properties measurement system with a closed-cycle cooling system. Dual-beam focused ion beam（FIB） system was used not only for preparing TEM samples but also depositing the metal electrodes. Micro-Raman（u-Raman） and photoluminescence（PL）were carried out the characterization of optical property.
The main focus of this dissertation can be divided into three parts. First, the electrical property of a single GaN nanowire was studied utilizing a home-made electrical property measurement system with a closed-cycle cooling system. Temperature-dependent resistance curves can be analyzed to identify the electrical transport mechanism. The electrical-transport reveals thermal activation and nearest-neighbor hopping behavior. The activation energy EA may be determined 8.42 meV, this smaller energy is suggested to due to a surface conduction channel. Moreover, electrons transport by nearest-neighbor hopping with energy of 39.93 meV.
In the second part, C-AFM was used to characterize the photoelectric properties of an individual defective GaN nanowire prepared without catalysts by thermal chemical vapor deposition. The current-voltage curve exhibits two clear negative differential resistance（NDR） regions in the forward bias. Moreover, sub-band-gap photocurrent was measured under illumination on the nanowire. The intrinsic defects introduced additional states in the band-gap resulting in the peculiar behavior of NDR and sub-band-gap photocurrent. Scanning electron microscopy（SEM） and transmission electron microscopy（TEM） were employed to characterize the morphology and microstructure. Cathodoluminescence spectrum of this GaN nanowire confirms the existence of the defects providing the below-gap emissions.
In the last part, oriented, bicrystalline GaN pyramid networks have been synthesized without catalyst by a thermal CVD method on Si(111) with a 300nm-thick GaN buffer layer. Selected area electron diffraction (SAED) and HRTEM observations indicate that the bicrystalline structure is composed of (0001) planes and the twin angle is about 118.7°. The bicrystalline structure mirrors along the [01-11] axis with a few angle shifts of ~ 5°. Raman spectra reveal the local vibration mode（LVM）due to vacancies at 420 cm^-1 and the surface mode at 709.8 cm^-1 for pyramid sample. Temperature-dependent PL were performed on the GaN buffer film and pyramid networks. Both sample reveal a dominant near band emission at room temperature, and become weaker at low temperature. The spectra of the pyramid exhibit the unusual peaks at ~3.230 and 3.182 eV at low temperature, which represent the luminescence of excitons bond to structural defects.

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