隨著光電產業的蓬勃發展，氧化鋅(ZnO)在光電材料應用方面也隨之增廣。本質氧化鋅為 n 型的半導體氧化物，如果能成功研發 p 型的氧化鋅與n型的氧化鋅搭配，將可開發氧化鋅於光電元件中全新的應用領域。但目前最大問題在於 p 型氧化鋅的製作，因氧化鋅本身會有自我補償(self-compensating)效應與摻雜之元素於氧化鋅中低溶解度等問題。因此本研究對氧化鋅薄膜及元件做一系列探討，主要分為以下四大部分，第一部分為射頻磁控濺鍍法製備鋰摻雜氧化鋅薄膜。第二部分為利用同步輻射分析薄膜性質。第三部分為製備氧化鋅異質接面元件。第四部份為製備氧化鋅同質接面元件。
首先以射頻磁控濺鍍法，藉由改變不同鋰之摻雜濃度，探討濺鍍參數對薄膜的影響。完成薄膜製備後進行不同溫度(350~550℃)之氬氣氛退火處理，使其進一步改善薄膜的性質。本研究以同步輻射分析，對於不同鋰摻雜含量之氧化鋅薄膜之局部原子排列與鄰近原子之電子能態結構逐一做分析，例如吸收原子之鄰近原子數、鄰近原子種類、吸收原子與各鄰近原子層之鍵長以及電子能態結構等訊息。從半導體應用的觀點，一般最基本的半導體結構型式即是 p-n 接面的結構，目前 p-n 異質接面二極體主要由 n 型氧化鋅結合穩定 p型透明導電材料。因此本研究利用氧化鎳薄膜結合氧化鋅薄膜製備p-NiO/n-ZnO異質接面元件，再利用I-V量測系統探討元件之特性。本研究最後並製備氧化鋅薄膜之n-ZnO/p-ZnO:Li同質接面透明導電氧化物元件，並藉由p-NiO/n-ZnO異質接面元件之經驗，引入於n-ZnO/p-ZnO同質接面元件。若能成功製備出以ZnO為基礎材料的透明導電氧化物元件，將會使半導體產業帶來嶄新的應用發展方向。
實驗結果顯示，鋰摻雜氧化鋅薄膜，出現C軸(002)優選方向，經退火處理過後薄膜結晶優選方向更加明顯。在不同鋰掺雜濃度下，薄膜之穿透率在可見光範圍平均達70%以上，薄膜光學能隙(Eopt)隨摻雜量增加而窄化現象產生。經過退火之後，穿透率皆有提高，最高約為80%。經由450℃的後熱處理，鋰摻雜氧化鋅薄膜呈現 p 型導電性質，具有最低之電阻率為0.11 ohm-cm，電子濃度及移動率分別為3.13×1018 cm-3 及2.2 cm2/Vs。由此可知，藉由摻雜鋰原子進入氧化鋅薄膜中之方法，雖然能改善氧化鋅薄膜的導電率，但降低薄膜的穿透率。由XANES實驗數據分析結果可知氧化鋅薄膜經添加不同鋰摻雜濃度後，並不會改變其鋅價數(Zn2+)及晶型結構。由EXAFS之數據中顯示，未添加鋰之氧化鋅薄膜其氧配位數為4.018，Zn-O鍵長為1.971 Å，而添加不同比例之鋰後，由結構參數特性顯示，添加鋰會造成配位數及鍵長的改變。最後利用磁控射頻濺鍍系統，組成氧化鋅薄膜之 p-n 同/異質接面後，藉由鋁做為金屬電極，利用I-V量測系統探元件之I-V特性。由I–V曲線顯示同/異質接面皆具有整流特性。實驗結果顯示，p-NiO/n-ZnO異質接面元件，可得到較佳的穿透率、較大的光響應比以及較快的光響應時間。

In the growing industry of photoelectric devices, ZnO is extensively used as the photoelectric material. The native ZnO films show n-type semiconductor behavior as the microstructure defects are carefully controlled. If the p-type ZnO films can be successfully made, the application scope will be further enlarged. It is difficult to achieve controllable p-type carrier doping of ZnO thin films, due to self-compensation effect of the opposite charge carriers and low solubility of the doping acceptors. Therefore, understanding the behaviors of defects in ZnO is a very important subject. Four issues investigated in this study are (1) the effects of deposition and annealing parameters on the structural, electrical and optical properties of ZnO:Li films; (2) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were used to observe the influence of Li-doped ZnO films, and tried to understand the relationship between electronic structure and the properties of the films; (3) the effects of deposition parameters on the structural properties of p-NiO/n-ZnO heterojunctiondevice;(4) the effects of deposition parameters on the structural properties of ZnO-based homojunction device.
In this work, lithium-doped ZnO (ZnO:Li) films were grown on glass substrates by r.f. reactive magnetron sputtering. We used different Li doping concentrations and various sputtering parameters to evaluate on the characteristics of thin films. The sputtered films were subsequently annealed at different temperatures (350~550℃) in argon ambient to further modulate their properties. The conductive mechanism and the microstructure defects are very important for stable p-type ZnO:Li films but still unknown. We will use an X-ray absorption near-edge structural (XANES) and extended X-ray absorption fine structural (EXAFS) spectroscopy to study the atomic defect information in the p-type ZnO:Li films and concluded the possible conductive mechanism. EXAFS has been accredited as a precise method for molecular structural characterization. It could provide the information on the atomic structure around the specific atom (in this experiment, it is Zn atom), such as near-neighbor atom distance and the fluctuation in bond length, which allows us to understand the essential mechanism of p-type behavior of ZnO:Li. The p–n junction is widely-adopted structure for UV photodetector. A number of p–n heterojunction have been reported by combining n-type ZnO with other p-type materials such as NiO, CuAlO2, CuGaO2, SrCu2O2, and AgInO2. Based on these results, the p-NiO/n-ZnO heterojunction devices are prepared by magnetron sputtering for UV photodetector. In addition, the recent research of ZnO/NiO heterojunctions in UV-detector also attracts many interesting attentions. Besides, the fabrication of ZnO-based homojunction using p-type ZnO films indicates the extensive applications of ZnO.
The experimental results reveal that all ZnO:Li films have (002) c-axis preferred orientation,which is more intensive after annealing. Regarding the optical properties, the transparency of the ZnO:Li film is about 70% in average during the visible spectrum. The optical band gap decreases with increasing the doping concentration of Li, indicating that the optical band gap of film is narrowing. After annealing, the film transparency increases and the highest one is about 80%. After annealing at 450℃, the lowest resistivity of 0.11 ohm-cm is obtained with the hole concentration and mobility of 3.13×1018 cm-3and 2.2 cm2/Vs , respectively. In conclusion, doping Li into ZnO films can improve the electrical conductivity, but lower the transparency. Annealing process, in contrast, enhances the film transparency but reduces the electrical conductivity. Without doping Li into the ZnO thin films, the coordination numbers (CN) of Zn atom and crystal structure are not changed. EXAFS spectra also indicate that the CN and the bond distances are 4.018 and 1.971 Å respectively. EXAFS analysis of ZnO:Li shows that the CN and bond distances are notably changed due to the incorporation of Li. Finally, high quality p-type ZnO:Li and n-type ZnO thin films are grown on glass substrates using r.f. reactive magnetron sputtering. For the analysis of homojunctions device, use Al as the metal electrode for I-V measurement. Results show that the homo/hetero-junctions device has good rectification characteristic. As a result, there are some better performance of the responsivity, rejection ratio and light transmission on the p-NiO/n-ZnO heterojunction structure.

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