本論文著重在於以電化學蝕刻法製備多孔隙薄膜，透過不同的參數控制達到不同形貌的薄膜，並將多孔隙應用在氣體感測之應用。
矽(Si)是地球上含量第二豐富的材料，目前已經大量被研究與應用。因次其低成本及良好的本質特性，已經被廣泛應用在半導體產業。近期，隨著能源議題，矽被致力研究於太陽能產業及電池產業上。多孔結構使得電性極佳的矽基板有半導體的性質，且有較大的表面積，獨特的電學性質及光學性質。此外，更能輕易達到大面積(15cm×15cm)的製程。由於製備過程簡易且整體成本較低，因此是非常好的應用材料。其較大的表面積且特殊的電性可以應用在氣體感測上，例如濕度感測、氫氣感測、有機氣體感測、氰化物感測。本文將金電極度在多孔矽薄膜上，利用不同參數的多孔薄膜，探討如何得到最敏感的一氧化氮氣體感測，而施加紫外線光可以使得氣體感測的反應更明顯。

Silicon, the second most abundant material on earth, has been applied on wide range regimes such as, batteries, semiconductor, and solar cell. Because of its low cost and well-developed technology, silicon can be used in many application. Porous silicon (PSi), due to its intrinsic property or the porous structure, has been presented to be fabricated by electrochemical etching.
For the lithium-ion batteries(LIB), the high theoretical capacity for Si is 3597 mAhg-1. However, the volume expansion during lithiation/delithiation limits its cycling performance. The PSi has been exploited to lithium-ion batteries with excellent capacitance, columbic efficiency, and cycling retention.
Recently, PSi has drawn considerable attention for sensor applications because of Its luminescence properties, large surface area, and compatibility with silicon-based technologies. Chemical functionalization of the large surface areas, which can be generated in PSi, show the potential for developing a variety of gas sensors. For this work, the PSi layer apply on NO sensor, and use the UV light to improve the performance. It can easy tell the different concentration of the NO from 0.25 ppm to 5 ppm, and the limit of detection (LOD) is 0.35 ppb.

Chapter 1 Introduction 5
1.1 Background 5
1.2 Porous silicon 6
1.2.1 Electrochemical etching of PSi 6
1.2.2 Properties and applications of porous silicon 10
1.3 Gas sensor 11
1.3.1 Porous silicon on sensing applications 11
1.3.2 Porous silicon on humidity sensor 12
1.3.3 Porous silicon on hydrogen detection 13
1.3.4 Porous silicon on NOx detection 14
1.3.5 The treatment of the porous silicon for gas sensor 16
1.3.6 Limit of detection (LOD) 16
Chapter 2 Experiment Instruments 19
2.1 Tube furnace 19
2.2 Scanning Electron Microcopy (SEM) 20
2.3 Experimental Design of The Measurement of the Gas Sensor 21
Chapter 3 Result and Discussion 23
3.1 Exfoliation of PSi thin films 23
3.1.1 The effect of the etching condition 23
3.1.2 The large scale of the electrochemical etching process 28
3.2 NO Gas Sensor with porous silicon 31
3.2.1 The UV apply on the gas sensor 31
3.2.2 The gas sensor in porous silicon layer with different etching condition 34
Chapter 4 Conclusions and Future Work 37
References 39
 

References
1. Masuko, K., et al., Achievement of More Than 25% Conversion Efficiency With Crystalline Silicon Heterojunction Solar Cell. Ieee Journal of Photovoltaics, 2014. 4(6): p. 1433-1435.
2. J Britt, C.F., Thin‐film CdS/CdTe solar cell with 15.8% efficiency. Applied Physics Letters, 1993. 62(22).
3. Green, M.A., et al., Solar cell efficiency tables (version 46). Progress in Photovoltaics, 2015. 23(7): p. 805-812.
4. BM, K., 27.6% conversion efficiency, a new record for single-junction solar cellsunder 1 sun illumination., in Proceedings of the 37thIEEE Photovoltaic Specialists Conference. 2011.
5. Ward, J.S., et al., A 21.5% efficient Cu(In,Ga)Se-2 thin-film concentrator solar cell. Progress in Photovoltaics, 2002. 10(1): p. 41-46.
6. Cruz-Campa, J.L., et al., Microsystems enabled photovoltaics: 14.9% efficient 14 mu m thick crystalline silicon solar cell. Solar Energy Materials and Solar Cells, 2011. 95(2): p. 551-558.
7. Branham, M.S., et al., 15.7% Efficient 10-mu m-Thick Crystalline Silicon Solar Cells Using Periodic Nanostructures. Advanced Materials, 2015. 27(13): p. 2182-+.
8. Li, G.J., et al., Nanopyramid Structure for Ultrathin c-Si Tandem Solar Cells. Nano Letters, 2014. 14(5): p. 2563-2568.
9. Radhakrishnan, H.S., et al., Improving the Quality of Epitaxial Foils Produced Using a Porous Silicon-based Layer Transfer Process for High-Efficiency Thin-Film Crystalline Silicon Solar Cells. Ieee Journal of Photovoltaics, 2014. 4(1): p. 70-77.
10. Abstreiter, G., et al., Strain-induced two-dimensional electron gas in selectively doped Si/Si x Ge 1− x superlattices. Physical Review Letters, 1985. 54(22): p. 2441.
11. Canham, L., K. Barraclough, and D. Robbins, 1.3‐μm light‐emitting diode from silicon electron irradiated at its damage threshold. Applied physics letters, 1987. 51(19): p. 1509-1511.
12. Canham, L.T., Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers. Applied Physics Letters, 1990. 57(10): p. 1046-1048.
13. Armand, M. and J.M. Tarascon, Building better batteries. Nature, 2008. 451(7179): p. 652-657.
14. Ozdemir, S. and J.L. Gole, The potential of porous silicon gas sensors. Current Opinion in Solid State and Materials Science, 2007. 11(5-6): p. 92-100.
15. Canham, L.T. Properties of porous silicon. 1997. Institution of Electrical Engineers.
16. Zhang, X.G., S.D. Collins, and R.L. Smith, Porous Silicon Formation and Electropolishing of Silicon by Anodic Polarization in Hf Solution. Journal of the Electrochemical Society, 1989. 136(5): p. 1561-1565.
17. Memming, R. and G. Schwandt, Anodic Dissolution of Silicon in Hydrofluoric Acid Solutions. Surface Science, 1966. 4(2): p. 109-&.
18. Turner, D.R., Electropolishing Silicon in Hydrofluoric Acid Solutions. Journal of the Electrochemical Society, 1958. 105(3): p. C55-C56.
19. Beale, M.I.J., et al., Microstructure and Formation Mechanism of Porous Silicon. Applied Physics Letters, 1985. 46(1): p. 86-88.
20. Lehmann, V. and U. Gosele, Porous Silicon Formation - a Quantum Wire Effect. Applied Physics Letters, 1991. 58(8): p. 856-858.
21. Föll, H., et al., Formation and application of porous silicon. Materials Science and Engineering: R: Reports, 2002. 39(4): p. 93-141.
22. Are electrical properties of an aluminum–porous silicon junction governed by dangling bonds? Applied Physics Letters, 1995. 67(11): p. 1570-1572.
23. Gole, J.L. and S.E. Lewis, Porous Silicon–Sensors and Future Applications, in Nanosilicon. 2008, Elsevier. p. 149-175.
24. Björkqvist, M., et al., Characterization of thermally carbonized porous silicon humidity sensor. Sensors and Actuators A: Physical, 2004. 112(2-3): p. 244-247.
25. Rittersma, Z., et al., A novel surface-micromachined capacitive porous silicon humidity sensor. Sensors and Actuators B: Chemical, 2000. 68(1-3): p. 210-217.
26. Björkqvist, M., et al., Comparison of stabilizing treatments on porous silicon for sensor applications. physica status solidi (a), 2003. 197(2): p. 374-377.
27. Arakelyan, V., et al., Hydrogen sensitive gas sensor based on porous silicon/TiO2− x structure. Physica E: Low-dimensional Systems and Nanostructures, 2007. 38(1-2): p. 219-221.
28. Rahimi, F. and F. Razi, Characterization of porous poly-silicon impregnated with Pd as a hydrogen sensor. Journal of Physics D: Applied Physics, 2004. 38(1): p. 36.
29. Rahimi, F., Characterization of Pd nanoparticle dispersed over porous silicon as a hydrogen sensor. Journal of Physics D: Applied Physics, 2007. 40(23): p. 7201.
30. Air Pollution Control Act. 2012.
31. Massera, E., et al., Improvement of stability and recovery time in porous-silicon-based NO2 sensor. Sensors and Actuators B: Chemical, 2004. 102(2): p. 195-197.
32. Boarino, L., et al., NO2 monitoring at room temperature by a porous silicon gas sensor. Materials Science and Engineering: B, 2000. 69: p. 210-214.
33. Chakane, S., A. Gokarna, and S. Bhoraskar, Metallophthalocyanine coated porous silicon gas sensor selective to NO2. Sensors and Actuators B: Chemical, 2003. 92(1-2): p. 1-5.
34. Baratto, C., et al., A novel porous silicon sensor for detection of sub-ppm NO2 concentrations. Sensors and Actuators B: Chemical, 2001. 77(1-2): p. 62-66.
35. Lewis, S.E., et al., Sensitive, selective, and analytical improvements to a porous silicon gas sensor. Sensors and Actuators B: Chemical, 2005. 110(1): p. 54-65.
36. Thai, D.L., et al., High Performance Three-Dimensional Chemical Sensor Platform Using Reduced Graphene Oxide Formed on High Aspect-Ratio Micro-Pillars. Advanced Functional Materials, 2015. 25(6): p. 883-890.
37. Sberveglieri, G., S. Groppelli, and P. Nelli, Highly sensitive and selective NOx and NO2 sensor based on Cd-doped SnO2 thin films. Sensors and Actuators B: Chemical, 1991. 4(3-4): p. 457-461.
38. Koshizaki, N. and T. Oyama, Sensing characteristics of ZnO-based NOx sensor. Sensors and Actuators B: Chemical, 2000. 66(1-3): p. 119-121.
39. Sadaoka, Y., T. Jones, and W. Göpel, Fast NO2 detection at room temperature with optimized lead phthalocyanine thin-film structures. Sensors and Actuators B: Chemical, 1990. 1(1-6): p. 148-153.
40. Miura, N., et al., Development of high-performance solid-electrolyte sensors for NO and NO2. Sensors and Actuators B: Chemical, 1993. 13(1-3): p. 387-390.