Dr. Bill McMahon received a bachelor's degree in engineering physics from the Colorado School of Mines in 1989, and a doctorate in physics from the University of Illinois, Urbana-Champaign in 1996. McMahon began his research career at NREL in 1995 by conducting scanning tunneling microscope (STM) studies of the atomic structure of MOCVD-prepared semiconductor surfaces used in III-V growth on Si and Ge surfaces. This work revealed a new strain-induced step structure and contributed to the development of world-record-efficiency GaInP/GaAs/Ge triple-junction solar cells. He has performed more recent research in collaboration with NREL's Computational Materials Science team, probing the atomic structure of dislocations in III-V materials. One key finding explains how ordering of III-V alloys can increase the glide force on dislocations. This result affects every aspect of dislocation nucleation and glide in ordered III-V materials. It also provided critical guidance for the design of the lattice-graded buffer layers used in high-efficiency 4-junction inverted metamorphic solar cells. McMahon has also led investigations into more applied aspects of multijunction cell performance and design, including cell bonding, nano-imprinted optical coatings, distributed resistance modeling of 3-D current flow in multijunction solar cells, and spectrally sensitive energy-yield measurement and modeling.
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