Bill McMahon has conducted research at NREL for more than 25 years.  During this time, he has performed foundational research on a wide range of topics impacting the growth, fabrication, and performance of high-efficiency III‑V solar cells.  

As a postdoctoral researcher, he studied the atomic structure of MOCVD-prepared semiconductor surfaces used in III‑V growth on silicon and germanium surfaces.  His research into the atomic structure of dislocations explained how ordering of III-V alloys can increase the glide force on dislocations, impacting the growth of lattice-mismatched solar cells.  He has also led investigations into cell bonding, nano-imprinted optical coatings, distributed resistance modeling of 3-D current flow in multijunction solar cells, and energy-yield measurement and modeling. 

Currently, his two main research areas are:  (1) developing foundational knowledge for the design, characterization and measurement of three-terminal solar cells and voltage-matched strings; and (2) using a fundamental understanding of dislocation formation in coalescing materials to direct projects investigating III-V growth on inexpensive and reusable substrates.

Education

Ph.D., Physics, University of Illinois, Urbana-Champaign

M.S., Physics, University of Illinois, Urbana-Champaign

B.S., Engineering Physics, Colorado School of Mines

Featured Work

A Taxonomy for Three-Terminal Tandem Solar Cells, ACS Energy Letters (2020)

Perspective: Fundamentals of Coalescence-Related Dislocations, Applied to Selective-Area Growth and Other Epitaxial Films, APL Materials (2018)

High-Temperature Nucleation of GaP on V-Grooved Si, Crystal Growth & Design (2020)

Growth of Antiphase-Domain-Free GaP on Si Substrates by Metalorganic Chemical Vapor Deposition Using an in situ AsH3 Surface Preparation, Applied Physics Letters (2015)

Control of Misfit Dislocation Glide Plane Distribution during Strain Relaxation of CuPt-Ordered GaInAs and GaInP, Journal of Applied Physics (2012)

Ordering-Enhanced Dislocation Glide in III-V Alloys, Journal of Applied Physics (2013)

Fill Factor as a Probe of Current-Matching for GaInP2/GaAs Tandem Cells in a Concentrator System during Outdoor Operation, Progress in Photovoltaics: Research and Applications (2008)

Strain-Driven Mesoscopic Reconstruction of the As/Ge(111) Surface, Physical Review Letters (2002)

Steps on As-Terminated Ge(001) Revisited: Theory versus Experiment, Physical Review Letters (2001)

5-7-5 Line Defects on As/Si(100): A general Stress-Relief Mechanism for V/IV Surfaces, Physical Review (2006)