Photodetectors and photovoltaic devices based on semiconductor nanomaterials

Photodetectors based various nanostructures and plasmon enhanced solar cell s e investigated in this dissertation. The motivation of the dissertati on rise is driven by urgent need of both high efficiency photodetectors and solar cells. First, quantum dot infrared photodetectors have been intensely investigate d due to their promise in high performance photodetectors. However, the strain-driven growth of quantum dots has hindered the progress of quantum dot photodetectors. The presence of strain in the device presents complexity in designing as well as defects. Therefo r , in this project, new designs of quantum dot photodetector structures are presented to improve the control over detection wavelength. Moreover, strain-free nanomaterials are incorporate d in the photodetectors for the first time in order to replace conventional strained quantum dots. By using the novel designs and nanomaterials, multicolor photodetector has been demonstrated. Based on t hese studies, high efficiency photodetectors may be achieved. Second, the increasing energy consumption of limited natural energy r sources has brought urgent requirement of sustainable and renewable energy resour ces. Solar energy directly from the Sun is promising in solving current energy crisis. In orde r to serve as a primary energy source, solar energy has to be harvested efficiently and be cost ef fectiv . Therefore, increasing the conversation efficiency beyond current technologies is high prio rity n current photovoltaics field. In this project, surface plasmonic effects are investiga ted for possible application in high efficiency quantum dot solar cells. Quantum dots have been widely us d to implement high efficiency intermediate band solar cells. Due to the low absorpti on in quantum dots, the performance of quantum dot solar cells has been unsatisfying. In t his dissertation, potential applications of surface plasmon in implement of intermediate band s olar cell are experimentally studied. Significantly, overall conversion efficiency of quantum dot sol ar cell has been improved for over 2%. More importantly, further enhancement is expected afte r op imization of design of plasmonic quantum dot solar cells. This dissertation provides a way t o effectively harvest the solar energy in the infrared wavelength region. This dissertation is approved for recommendation to the Graduate Council Dissertation Director: ____________________________________ Dr. Omar Manasreh Dissertation Committee: ____________________________________ Dr. Simon Ang ____________________________________ Dr. D. Keith Roper ____________________________________ Dr. Shui-Qing Yu DISSERTATION DUPLICATION RELEASE I hereby authorize the University of Arkansas Libraries to duplic ate this dissertation when needed for research and/or scholarship. Agreed ________________________________________ Jiang Wu Refused ________________________________________ Jiang Wu ACKNOWLEDGEMENTS First and foremost, I would like to thank my parents for their love and support. The thanks to them are beyond any words. I would like to thank my wife, Sil u Li, for her constant love, support, patience, and confidence in me. Without her, I can not have moved so far. I express my deepest gratitude to my parents-in-law and grandparents for the ir l ve. I would like to express my gratitude to my chair advisor and project director, Dr. Omar Manasreh, for his guidance throughout my graduate project. The resear ch tr inings I have received in the Optoelectronics Research Lab directed by Dr. M anasreh have been and will be valuable for my career. The knowledge I have learned from Dr. M anasreh is beyond research fields. I am extremely grateful of Dr. Simon Ang, Dr. Keith Roper, and D r. Shui-Qing Yu for being in my committees and helping me to complete this project. I a m gr teful for the valuable support from my doctoral committee members, Dr. Simon Ang, Dr. Keit h Roper, and Dr. ShuiQing Yu. I would like to express my special thanks to my research collea gues, Dr. Brandon Passmore and Dr. Eric DeCuir, Jr., for the all the help and support dur ing my graduate study. Sincere thanks go to Dali Shao, Scott Mangham, Seungyong Lee, Dr. Va nga Reddy, Rick Eyi, David Fryauf, Shibin Li, Xin Yan, Da Zhuang, and James Gilboy for their help during my study. I would also like to thank other group members who might be omitted here for their help. I would like to thanks Dr. Bradly Weaver at Naval Research Labor atory for his collaboration with us. I would like to thanks Dr. Salamo, Dr. Zhiming W ang, Dr. Vasyl Kunets, and Dr. Zhaoquan Zeng for training me on MBE. I would also like to t hank Dr. Mourad Benamara for the training of electron microscopes and helps in my project. The work at University of Arkansas is supported by the Air Forc e Office of Scientific Research (grant no. FA9550-10-1-0136), the National Science Foundation (gr ant no. EPS1003970), Arkansas Science & Technology Authority, and collaboration with N aval Research Lab which is supported by a grant from the Naval Research Office. Finally, I would like to thank the University of Arkansas Graduate S chool for the Doctoral Academy Fellowship during this project.