臺灣博碩士論文加值系統

本論文利用射頻磁控濺鍍法將氧化鎵與氧化鎵鋅薄膜沉積於藍寶石基板上，因為此氧化物半導體有相當寬的能隙，可以被應用在深紫外光偵測器元件。本研究將氧化鎵與氧化鎵鋅薄膜製作成金屬-半導體-金屬結構的光偵測器元件。我們以氧化鎵薄膜爲對照組，藉由改變基板溫度、成長氣氛(氬氣、氧氣)、退火溫度及退火氣氛等條件，將氧化鎵鋅薄膜與元件特性最佳化。
本研究首先探討基板溫度對薄膜性質與元件特性的影響，基板溫度從室溫逐漸改變至600 °C，並在純氬氣氛圍製備氧化鎵鋅薄膜。X光繞射分析得知，當基板溫度高於400 °C時，氧化鎵鋅薄膜才會出現結晶相。接著將薄膜製作成光偵測器，當元件使用基板溫度400 °C成長的氧化鎵鋅薄膜製作時，在照射光波長240 nm與偏壓5V量測條件下，其最大光響應度值可達0.7 A/W。結果推測與純氬氣製程可能產生氧空缺有關。
本論文接著探討成長過程中調變氬氣與氧氣比例對於氧化鎵鋅薄膜的影響。結果發現，當製程中通入氧氣時，薄膜結晶性明顯變差；且這些薄膜製作成光偵測器的光電流明顯降低，使得元件響應度變差。
上述結果可知利用基板溫度400 ℃及純氬氣氛圍下成長的氧化鎵鋅薄膜製備成光偵測器時，具有最好的元件特性。為了進一步改善元件特性，將最佳成長條件的氧化鎵鋅薄膜進行退火處理。結果發現在適當的退火溫度處理後，氧化鎵鋅薄膜結晶特性可提升。在光偵測器的部分，退火溫度為700 ℃與大氣氛圍下退火處理的的氧化鎵鋅元件，有較大的光電流( 2.02×10-7A )與較低的暗電流( 5.35×10-12A )，其最大光響應度值為2.53 A/W(在照射光波長240 nm與偏壓5V量測條件下)。
在退火氣氛調變的實驗中，發現氧化鎵鋅薄膜在真空下退火會使薄膜的氧空缺增加，可提升元件的光電流，但也造成暗電流變大；在純氧氣氛圍下退火，則會使薄膜內氧空缺減少，因此暗電流降低，同時使得光電流降低，並導致響應度下降。在大氣下退火可修補薄膜內氧空缺，因此元件有最佳的光暗電流比與最佳的響應度，比起對照組之氧化鎵薄膜感測器，其頻譜峰值可藍移至240 nm，且響應度更高。

In this thesis, ZnGa2O4 thin films were prepared on c-plane sapphire substrates by RF sputtering. Due to its wide bandgap, ZnGa2O4 films can be used for fabricating the metal-semiconductor-metal (MSM) deep ultraviolet photodetectors (DUVPDs). The sputtered Ga2O3 films were used as the reference samples for comparison. By adjusting the process parameters such as substrate temperature, gas atmosphere for growth, annealed temperature and annealed atmosphere, the characteristics of ZnGa2O4 films and optoelectronic performances of DUVPDs can be optimized.
Firstly, ZnGa2O4 thin films were deposited in Ar atmosphere at various substrate temperatures (RT to 600 °C). Based on the x-ray diffraction (XRD) results, when the substrate temperature was higher than 400 °C, the crystal structure of ZnGa2O4 film was transformed from amorphous to crystalline. These ZnGa2O4 films deposited at various substrate temperatures were then used as the active layers to fabricate the PDs. Among these devices, the PD prepared with the 400 °C-grown ZnGa2O4 film possessed better optoelectronic performances. At a bias voltage of 5 V and 240-nm irradiation, this PD possessed a larger photocurrent of 5.69×10-8 A, a smaller dark current of 5.77×10-12 A, and a higher responsivity of 0.7 A/W.
More oxygen vacancies may be generated in the film when the pure argon atmosphere was used during the growth process. Subsequently, the oxygen gas was properly introduced in the growth process, and the effect of argon/oxygen ratio on the film’s properties was investigated. XRD analysis shows that the crystallinity of the film is lowered by introducing the oxygen gas. Additionally, after adding the oxygen gas in the growth process, the PDs with these films have both lower photocurrents and photoresponses in comparison to those with the film grown in pure argon atmosphere.
Based on the above results, the substrate temperature of 400 °C and the pure argon atmosphere are the optimum growth conditions for fabricating the ZnGa2O4 PD. To further improve the device characteristics, the thermal annealing treatment was performed on the as-deposited ZnGa2O4 film. After thermal annealing at suitable temperatures in air atmosphere, the film’s crystallinity can be improved. After fabricating the PD with the 700 C-annealed film, the device performances are enhanced, which has a photocurrent of 2.02×10-7A, a dark current of 5.35×10-12A, and a responsivity of 2.53 A/W (@5 V and 240 nm).
Finally, via the adjustment of annealing atmosphere, it can be found that the device performance is mainly affected by the oxygen atmosphere. When the film was annealed in vacuum, the content of oxygen vacancy was increased, leading to both increments in the photocurrent and dark current of fabricated PD. Moreover, as the pure oxygen atmosphere was used in the annealing process, the content of oxygen vacancy of the film was reduced, which resulted in an effective decrease in the dark current of fabricated PD. However, the photocurrent and responsivity of this device both reduced. When the annealing process was performed in air atmosphere, the fabricated PD had the optimum optoelectronic performances including the photo/dark current ratio and responsivity. Moreover, the spectral response peak showed a blue shift to 240 nm and higher responsivity data as compared with those of the Ga2O3 photo detectors.

誌謝 i
摘要 ii
Abstract iv
圖目錄 x
表目錄 xiv
第一章 緒論 1
1-1前言 1
1-2寬能隙半導體的優勢與應用 2
1-2-1 寬能隙材料特性 2
1-2-2 寬能隙半導體之應用 3
1-2-3 寬能隙半導體深紫外光感測器 4
1-3 研究動機 6
1-4 論文架構 8
第二章 文獻回顧 9
2-1 氧化鎵材料特性與應用 9
2-1-1 氧化鎵材料特性 9
2-1-2 氧化鎵元件應用 10
2-2 氧化鎵鋅磊晶研究 10
2-3 濺鍍原理 12
2-3-1 電漿 12
2-3-2 磁控濺鍍 12
2-3-3 射頻濺鍍 13
2-4 光偵測器元件 13
2-4-1 紫外光MSM結構(solar-blind)光偵測器元件 15
第三章 實驗步驟與方法 16
3-1 實驗流程 17
3-2 使用射頻磁控濺鍍技術成長氧化鎵鋅薄膜參數 17
3-2-1 測試基板溫度對氧化鎵鋅光偵測器的影響 17
3-2-2 測試製程氣氛退火溫度對氧化鎵鋅薄膜的影響 18
3-2-3 測試退火溫度對氧化鎵鋅薄膜的影響 18
3-2-4 測試退火氣氛對氧化鎵鋅薄膜的影響 18
3-7 光偵測器製作 18
3-7-1 定義電極圖形 19
3-7-2 指叉電極金屬沉積 19
3-4 製程設備 20
3-5 實驗分析 20
3-5-1 X光繞射分析儀 ( X-ray Diffraction Analysis ) 21
3-5-2 原子力顯微鏡 (Atomic force microscope) 22
3-5-3穿透式電子顯微鏡 (Transimmision Electron Microscope) 23
3-5-4 化學分析電子能譜 (Electron Spectroscopy For Chemical Analysis) 24
3-5-5 薄膜特性分析儀 (n&k Analyzer) 25
第四章 結果與討論 27
4-1 前言 27
4-2 基板溫度對氧化鎵鋅薄膜的影響 27
4-2-1 基板溫度對薄膜成長速率影響 27
4-2-2 基板溫度對薄膜特性影響 30
4-2-3 基板溫度對氧化鎵鋅光偵測器元件的影響 36
4-3 製程氣氛對氧化鎵鋅薄膜的影響 39
4-3-1 製程氣氛對薄膜特性影響 39
4-3-2 製程氣氛對氧化鎵鋅光偵測器元件特性影響 45
4-4 退火溫度對氧化鎵鋅薄膜的影響 47
4-4-1 退火溫度對薄膜特性影響 48
4-4-2退火溫度對氧化鎵鋅光偵測器元件的影響 54
4-5退火氣氛對氧化鎵鋅薄膜的影響 57
4-5-1 退火氣氛對薄膜特性影響 57
4-5-2 不同退火氣氛對薄膜元件特性影響 59
4-6 氧化鎵基材料應用於深紫外光感測器 61
4-7氧化鎵鋅/氮化鎵異質接面深紫外光感測器 62
第五章 結論與未來展望 64
參考文獻 65
論文著作 71

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