University of Arkansas, Fayetteville ScholarWorks@UARK Theses and Dissertations 12-2013 Zinc Oxide Nanorod Based Ultraviolet Detectors with Wheatstone Bridge Design Arun Vasudevan University of Arkansas, Fayetteville Follow this and additional works at: http://scholarworks.uark.edu/etd Part of the Electronic Devices and Semiconductor Manufacturing Commons, Nanoscience and Nanotechnology Commons, and the Semiconductor and Optical Materials Commons Recommended Citation Vasudevan, Arun, "Zinc Oxide Nanorod Based Ultraviolet Detectors with Wheatstone Bridge Design" (2013). Theses and Dissertations. 928. http://scholarworks.uark.edu/etd/928 This Dissertation is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of ScholarWorks@UARK. For more information, please contact [email protected], [email protected]. Zinc Oxide Nanorod Based Ultraviolet Detectors with Wheatstone Bridge Design Zinc Oxide Nanorod Based Ultraviolet Detectors with Wheatstone Bridge Design A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Microelectronics-Photonics By Arun Vasudevan University of Kerala Bachelor of Science in Physics, 2002 Cochin University of Science and Technology Master of Science in Physics, 2005 December 2013 University of Arkansas This dissertation is approved for recommendation to the Graduate Council. ______________________________ ______________________________ Dr. Taeksoo Ji Dr. Simon Ang Dissertation Director Dissertation Co-Director ______________________________ ______________________________ Dr. Z. Ryan Tian Dr. Shui-Qing (Fisher) Yu Committee Member Committee Member ______________________________ Prof. Kenneth Vickers Committee Member The following signatories attest that all software used in this dissertation was legally licensed for use by Arun Vasudevan for research purposes and publication. __________________________________ __________________________________ Mr. Arun Vasudevan, Student Dr. Simon Ang, Dissertation Co-Director This dissertation was submitted to http://www.turnitin.com for plagiarism review by the TurnItIn company’s software. The signatories have examined the report on this dissertation that was returned by TurnItIn and attest that, in their opinion, the items highlighted by the software are incidental to common usage and are not plagiarized material. __________________________________ __________________________________ Prof. Ken Vickers, Program Director Dr. Simon Ang, Dissertation Co-Director ABSTRACT This research work, for the first time, investigated metal-semiconductor-metal (MSM) zine oxide (ZnO) nanorod based ultra-violet (UV) detectors having a Wheatstone bridge design with a high responsivity at room temperature and above, as well as a responsivity that was largely independent of the change in ambient conditions. The ZnO nanorods which acted as the sensing element of the detector were grown by a chemical growth technique. Studies were conducted to determine the effects on ZnO nanorod properties by varying the concentration of the chemicals used for the rod growth. These studies showed how the rod diameter and the deposition of ZnO nanorods from the solution was controlled by varying the concentration of the chemicals used for the rod growth. Conventional MSM UV detectors were fabricated with ZnO nanorods grown under optimized conditions to determine the dependence of UV response on electrode dimension and rod dimension. These studies gave insights into the dependence of UV response on the width of the electrode, spacing between the electrodes, density of the rod growth, and length and diameter of the rods. The UV responsivity was affected by varying the number of times the seed layer was spin coated, by varying the spin speed of seed layer coating and by varying the annealing temperature of the seed and rod. Based on these studies, optimum conditions for the fabrication of Wheatstone bridge UV ZnO nanorod detectors were determined. The Wheatstone bridge ZnO nanorod UV detectors were fabricated in three different configurations, namely, symmetric, asymmetric, and quasi-symmetric. The transient responses of the symmetric, asymmetric and quasi-symmetric configurations at room temperature and above showed how the response stability differed. At high temperature the responsivity of quasi-symmetric Wheatstone bridge detector configuration did not drop after saturation and the responsivity drifted by 17% to 25% from the room temperature response. The responsivity of the symmetric, asymmetric (rods in one quadrant), asymmetric (rods in three quadrant), and quasi-symmetric Wheatstone bridge was approximately 3.25 A/W, 0.95 A/W, 15.00 A/W, and 1.20 A/W and the corresponding response time was 299 sec, 71 sec, 217 sec, and 159 sec, respectively. The responsivity of quasi- symmetric Wheatstone bridge configuration with good temperature stability was 1.16 A/W, while those of conventional MSM UV detectors were approximately 60 A/W. However, the quasi-symmetric Wheatstone bridge with responsivity 1.16 A/W was higher than the commercially available detector having responsivity of only about 0.1 A/W. Though the response of quasi-symmetric Wheatstone bridge detector was higher than the detectors available commercially, the response time was very high. The response time of quasi-symmetric Wheatstone bridge was approximately 159 seconds at room temperature, while that of commercially available detectors is of the order of microseconds. If the quasi-symmetric Wheatstone bridge has to compete with current commercially available detectors, then the response time should be brought down from seconds to microseconds. Based on these studies, an improved design of the quasi-symmetric Wheatstone bridge UV detector with the ZnO rods oriented parallel to the substrate instead of oriented vertical to the substrate was proposed. ACKNOWLEDGMENTS At the outset I would like to thank my advisors Dr. Taeksoo Ji and Dr. Simon Ang for all the guidance, support, and extending all possible help to complete this research work. Being far away from home is emotionally hard and painful, but their humble and calm nature wiped away those hard feelings. I gained the initial momentum to push forward with this work only because of Dr. Soyoun Jung, former adjunct Assistant Professor of the Electrical Engineering, University of Arkansas, timely help and guidance. I would like to use this opportunity to thank her for being gracious enough to help me whenever it was needed. In academic or industry, a goal can be achieved only through meticulous planning and then try hard to stick with the plan, was the simple message and advice from the MicroEP Program Director, Prof. Kenneth Vickers. Though planning was easier, the hard part was to stick with the plan. But my attempt to do so helped me to achieve fruitful results and to finish my research work. I would like to thank Prof. Kenneth Vickers for reinforcing in me with this simple mantra for success. I would also like to thank Ph.D. defense committee members Dr. Ryan Tian and Dr. Fisher Yu for the few but fruitful discussions about my research work as well as my strength and weaknesses. I am especially thankful to them for pointing out to me my weakness. Their frank opinions did help me to focus on my weaknesses and I wholeheartedly did attempt to overcome them. During research, smooth working is only possible if you have sound technical experts to mitigate technical glitches as well as to impart the necessary training for using equipment. HIDEC staffs Dr. Mike Glover, Mr. Errol Porter, and Mr. Mike Steger, Institute of Nanoscience and Engineering staffs Dr. Mike Hawkridge and Dr. Mourad Benamara, former Science and Engineering staff Allan Toland, and Dr. Rob Sleezer were really helpful and they played this role really great. I am really grateful and would like to express my sincere thanks to all of them. Doing research as well us keeping track of other academic obligations was really difficult. But Mrs. Renee Hearon, MicroEP program specialist, made our life easier by keeping constant track of our academic obligations and reminding us whenever we failed to meet any obligations. I would like to express my heartfelt thanks to her for all the help and advices. I would like to thank my past mentors Rev. Father David Kandathil, Dr. Pradeep B., Mr. Anil Kumar and all the physics teachers of Cochin University of Science and Technology from 2003- 2009. They were the really architect of what I am today. Their motivation is the fuel for my life. They taught me the real purpose of life and inspired me to set goals in my life. I would like to express my sincere thanks to my dear friends Mr. Adarsh Chandu, Mr. Anil Xaviour, Mr. Anish Kumar, Mr. Arun Aravind, Mrs. Ashwathy V. S., Mr. Bevin George, Mr. Binumon P. K., Mr. Dharma Theja, Mr. Harish Goud, Mr. Jithesh Veetil, Mr. John George, Dr. Junais Habeeb, Mr. Kamalakar Gaddam, Mrs. Karthika R., Dr. Mirosh Thomas, Mr. Mythra Varun, Mr. Nikhil Thomas, Mr. Phaniraj Joshi, Mrs. Reena Rajan, Mr. Sai kishore, Mr. Sai Krishna, Mr. Sandeep Reddy Putta, Mr. Sasankakumar S., Ms. Shrijeetha Ganguly, Ms. Shruti Tripuraneni, Mrs. Sindhu Mirosh, Mr. Sundeep Chalamalasetty, Mr. Suraj Sujathan, Mr. Vinayaraj O. K., Ms. Vinayasree S., Mrs. Vineetha V. S., and Dr. Vivek A. K., for all the help and wonderful moments they gifted me. Last but not least I would like to thank my grandparents Mr. Narayanan Pillai and late Mrs. Sumathi