Gallium Arsenide Based Metal-Semiconductor-Metal Devices and Detectors A Thesis Submitted to the Faculty of Drexel University by Eric Michael Gallo in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering September 2010 c Copyright 2010 Eric Michael Gallo. All Rights Reserved. ii Dedications I would like to dedicated this work to Gavin, Riley, Ethan, Greg and Jesjka for inspiring me to continue to strive to be someone to look up to. iii Acknowledgments This work would not have been possible without the generous support of my advisor Dr. Jonathan Spanier. His patience with me has been infinite and his ability to help get to the root of research problems has been invaluable. I would also like to thank Dr. Bahram Nabet for his advising and guidance early in graduate career and for presenting me with the opportunity to learn and pursue many different aspects of device physics. Much of the work presented is the result of long standing collaborations with several researchers. I would like to acknowledge Adriano Cola and Fabio Quaranta for fabrication and measurements on the 2DEHG devices, Marc Currie of NRL for high speed optical characterization measurements, Nico Lovergine, Paula Prete and the rest of their lab for growth of the GaAs nanowire structures. I would like to acknowledge those who contributed to this work at Drexel including my labmates: Dr. Xia Zhao and Dr. Xiying Chen both of whom contributed heavily to the work presented and were strong mentors to me as a young graduate student. I would like to thank Sean Chen for his tireless hours of work on the nanowire devices along with his tireless hours of discussion with me on the results and the philosophy of science. I would also like to thank my other labmates for their contributions in device fabrication and characterization: Oren Leaffer, Terrence McGuckin, Stephanie Johnson, Brian Beatty, Mike Coster, Jennifer Atchison, Joan Burger, Rob Crow, Ron Martin, Sourav Das, Lee Laim, Linyou Cao, Zakiya Carter, Bora Garipcan and Stephen Nonnenmann. I would also like to acknowledge Yale Goldman, Joseph Forkey, Moshe Kam, Allen Rothwarf, Tim Kurzweg, Eli Fromm, Robert Quinn, Kevin Scoles, Roberto Cingolani, Alan MacDiarmid, Charlie Johnson and Ed Gerber for mentoring me during my years as a graduate student. Their guidance and encouragement has helped me grow not iv only as a researcher but also as a member of the academic community. Most importantly I would like to acknowledge the support of my family and friends, who maintained constant faith that I would finish even when I didn't be- lieve it myself. Thanks to my mother, Diane Gallo and my father, Frank Gallo for being incredibly supportive in my work and life. To my grandparents, Charles and Doris Makinson and Jean Gallo, for convincing me I was destined for great things. And to the rest of my family: Marj, Alana, Justin, Jon, Matt, Dave, Nick, Gavin, Ethan, Riley, Gregory, Jesjka, Baby, Maya and Harley for believing in me and lov- ing me unconditionally. I would also like to thank the Mullay Family: Kim, Nick, Carol, Vince and Steve for their support and inspiration. You are my hero Steve and continue to be an inspiration in all parts of my life. I would like to thank Linda Keglovits, Nancy Fritz and Glen Wallingford for instilling within me the confidence to pursue higher education. Their words and guidance still motivate me almost 20 years later. The path to a PhD has been a long and treacherous one for me and I could not have made it without the support of Simone Allender, who has been an amazing mentor and friend through the entire journey. Leah D'Agostino, Courtney McCarron and Kimberly Shannon have been and continue to be amazing and tolerant friends and insisting on taking care of me even when I don't believe I need it. I would also like to specifically thank: Adam O'Donnell, Michelle Sipics, Charlotte Lee, Denise McKellick, Marybeth Chew, Nicole VanNortwich for their unending support. I owe a debt of thanks to all of the individuals who kept life fun and interesting in Philadelphia: Adam Mancini, Jula Nawrocki, Bryan Allen, Eric Cronin, Carrieann Nielsen, Sean Fenton, Makaria Tsapatoris, Jason Haraldsen, Jenny Corbin, Jestis Deuerlein, Johna Winters, Joe McCleery, Rayna Bondy, Nick Kirsch, Margot Quin- lan, Gudrun Lubbe, Sue Oleykowski, Andrew Burnheimer, Markos Kapes, Shannon v Quinn, Shakey Lyman, Rich Mulhearn, Danno, Jon Eskow, Kristin Hanson, Decker, Mitch, Patti, Sky, Dawn, Stirling, Sienna, Elena, Ben, Aaron Henry, Monique Harris, Erika Hubbard, Nikoia Greene and everyone else that has made my life in Philadel- phia one to brag about. I would also like to add a special thank you to Doobies and Intermezzo. Last but not least, thank you to Andy and Henry for giving me that final push and helping me see everything there was to look forward to afterward. My career as a graduate student was supported by the National Foundation Grad- uate Student Fellowship, The Koerner Family Fellowship, The NSF GK-12 Graduate Fellowship and the Simone Allender Student Housing Fellowship. The nanowire work was supported by NSF-ECCS-0702716 and NSF-DMR-0722845 as well as US Army Research Office under the DURIP program in the form of instrumentation vi Table of Contents LIST OF TABLES .................................................................... viii LIST OF FIGURES ................................................................... ix ABSTRACT ........................................................................... xvii 1. Gallium Arsenide Based Electron Devices ....................................... 1 1.1 GaAs-Based Nanostructures ................................................ 1 1.2 Quantum well based material system ...................................... 3 1.3 Nanowire based material system............................................ 3 1.4 Objective and Scope of the Dissertation ................................... 4 2. Metal-Semiconductor-Metal Devices ............................................. 6 2.1 Metal-Semiconductor-Metal Structure ..................................... 6 2.2 MSM Band Diagram ........................................................ 6 2.3 Transport models ............................................................ 7 2.4 Sources of MSM Characteristics ............................................ 9 2.4.1 Semiconducting Material ............................................ 10 2.4.2 Metal-Semiconductor Interface ..................................... 12 2.4.3 Semiconductor Surface .............................................. 13 2.4.4 Substrate ............................................................. 14 2.5 MSM Detectors .............................................................. 14 2.5.1 Photodetectors ....................................................... 15 2.5.2 Molecular and Biological Species Detectors........................ 15 3. Two Dimensional Electron-Hole GaAs ........................................... 18 3.1 Heterostructure MSM ....................................................... 18 3.2 Two Dimensional Electron-Hole Gas Structure............................ 19 3.2.1 Coulomb Drag and Plasmonic Interaction ......................... 20 3.3 Design and Structure of the 2DEHG ....................................... 23 3.4 Simulated Band Structure................................................... 25 3.4.1 Confined States ...................................................... 25 3.4.2 Carrier Concentrations and Built in Electric Field................ 27 3.5 MSM Fabrication ............................................................ 28 3.6 Electrical Characterization Setup........................................... 29 3.7 Photoresponse................................................................ 30 3.7.1 DC Photoresponse ................................................... 30 3.7.2 Photocurrent Dependence on Wavelength ......................... 32 3.8 Capacitance-Voltage Measurements ........................................ 34 3.8.1 Capacitance Dependence on Wavelength .......................... 40 3.9 High Speed Photoresponse .................................................. 41 3.9.1 Measurement Setup ................................................. 41 3.9.2 Low Power Time Response ......................................... 42 3.9.3 Bandwidth of Measurement Setup ................................. 43 3.9.4 Higher Power Time Response....................................... 43 3.9.5 Response Dependence on Wavelength.............................. 47 vii 3.9.6 Analysis of Fall Times............................................... 48 3.9.7 Effects of Geometry ................................................. 48 3.9.8 Effect of Bias......................................................... 52 3.9.9 Discussion of Results ................................................ 53 3.10 Optical Characterization .................................................... 54 3.10.1 Reflectance ........................................................... 54 3.10.2 Calculation of Expected Radiative Transition Energies........... 55 3.10.3 Optical Measurement Setup ........................................ 57 3.10.4 Photoluminescence Results on Sample without Bragg ............ 58 3.10.5 Photoluminescence Results on Sample with Bragg................ 61 3.10.6 Analysis of Photoluminescence with Varying Incident Power .... 66 3.10.7 Analysis of Photoluminescence at Varying Temperature ......... 69 3.10.8 Photoluminescence Dependence on Focal Position ...............