本論文致力於研究氧化鎵奈米結構的成長特性，詳細探討材料及光電特性，並且應用於紫外光檢測器、氣體感測器、酸鹼度感測器、及電化學電解水產氫。
單斜晶系的氧化鎵(β-Ga2O3)為n型寬能隙(4.9 eV)半導體材料，具高耐熱性及良好的化學穩定性，在光電元件的應用上深具潛力。本研究中，利用化學氣象沉積，氣-液-固機制製備高品質單斜晶氧化鎵奈米線於二氧化矽/矽基板。隨著成長溫度增加，氧化鎵奈米線長度、密度、晶性及場發射特性都隨之提升。並藉由紫外光照射，氧化鎵奈米線的起始電場由
2 V/μm 減為 1.2 V/μm，增益因子(β)由4489增為 6926，這可歸因於較大的能帶扭曲和更多的電子積累，優越的場發射特性顯示其氧化鎵奈米線在元件應用上極具潛力。
在氧化鎵系列紫外光檢測器研製方面，探討不同成長溫度的氧化鎵奈米線，對其檢測器的影響，實驗結果顯示，擁有較佳晶性的氧化鎵奈米線光偵測器，有明顯的截止波長位於為255nm，在偏壓5V下，響應值可達3.43×10-3 A/W。
於氣體感測器應用，利用材料特性最佳的成長溫度950℃的氧化鎵奈米線製成異丙醇氣體感測器，探討不同操作溫度及不同的氣體濃度下的靈敏度。實驗結果顯示，在較低的操作溫度及較低的濃度下，仍有良好的靈敏度。
酸鹼度檢測器方面，我們首次利用氧化鎵奈米線製備延伸式閘極場效電晶體酸鹼度感測器。藉由奈米線結構提高反應面積，有效提升酸鹼度感測特性，電流及電壓感測度分別達15.8μA/pH及24.8 mV/pH，在pH量測方面展現出應用上之發展潛力。
光電化學電解水產氫部分，探討不同成長參數的奈米線，其電解水產氫效率，由研究結果發現照光產生的光電流與氧化鎵奈米線的形貌和晶性有絕對相關性，奈米結構提高工作電極與電解液之間有效反應面積，良好的晶性則可降低漏電流，增加光電流及產氫速率。我們也證實了氧化鎵的抗腐蝕性及發展光電化學電極的潛力。

In this thesis, the synthesis and characterization of Ga2O3 nanowires have been conducted. We also investigate the application for field emitter, photodetectors, gas sensor, pH sensor, and photoelectrochemical hydrogen generation.
Monoclinic Ga2O3 (β-Ga2O3) with bandgap energy of 4.9 eV has an excellent thermal and chemical stability potentially suitable for device applications. In this study, we report the vapor–liquid–solid (VLS) growth of β-Ga2O3 nanowires on the cost-effective SiO2/Si template by vapor phase transport. It was found that average length, density, quality, density, and field emission properties of the nanowires all increased as we increased the growth temperature. For the sample prepared at 950oC, the turn-on field from 2 V/μm reduce to only 1.2 V/μm while enhance the field-enhancement factor β from 4489 to 6926 by UV irradiation. It should be attributed to the larger band distortion and more electrons accumulation. The superior performances suggest that our Ga2O3 nanowires field emitters are potentially useful for device applications.
On the part of Ga2O3 photodetectors, using a different growth conditions to discuss the impact on the performance of Ga2O3 photodetectors. With an incident light wavelength of 255 nm and an applied bias of 5V, it was found that measured responsivity of the photodetector prepared at 950oC was 3.43×10-3 A/W.
In this section, detailed growth procedures and the isopropanol gas sensing properties of the fabricated device will also be discussed. With a large surface-to-volume ratio and high quality of Ga2O3 nanowires, it has been shown that nanowire-based gas sensors could provide a high sensitivity. The responses were measured at different operating temperatures and isopropanol gas concentrations. The superior performances suggest that the β-Ga2O3 nanowire gas sensor proposed in this study is potentially useful at low working temperatures.
For the fabrication of pH sensor, this is the first research to take show new possibilities to fabricate extended-gate field-effect transistors pH sensor by the synthesis of Ga2O3 nanowires. The sensitivity of the sensors could be quantified from the slope of the IDS - pH and the VREF - pH relations were 15.8 μA/pH and 24.8 mA/pH, respectively. This result suggested that the β-Ga2O3 nanowires are promising for designing high-performance pH sensors in virtue of their high surface areas for more surface binding sites and larger effective sensing areas.
On the part of photoelectrochemical hydrogen generation, it is observed that variations of the photocurrent with bias voltage depend strongly on the morphology and crystal quality of β-Ga2O3 nanowires in the electrolyte. The smaller dark current density observed from the sample prepared at 950℃ should again be attributed to the improved crystal quality. Three-electrode Photoelectrochemical efficiencies of Ga2O3 nanowires are 0.006%, 0.803%, and 1.684% at zero bias voltage for the samples grown at 850, 900, and 950oC respectively. An essential requirement of resistance to reactions such as photo-corrosion, electrochemical corrosion, and dissolution at the solid–liquid interface was demonstrated. The results suggest that the Ga2O3 nanowires can be applied to high-performance Photoelectrochemical devices.

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