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Growth of Metamorphic InGaP for Wide-Bandgap Photovoltaic Junction by MBE

Published online by Cambridge University Press:  01 February 2011

John Simon
Affiliation:
[email protected], Yale University, Electrical Engineering, New Haven, Connecticut, United States
Stephanie Tomasulo
Affiliation:
[email protected], Yale University, Electrical Engineering, New Haven, Connecticut, United States
Paul Simmonds
Affiliation:
[email protected], Yale University, Electrical Engineering, New Haven, Connecticut, United States
Manuel J Romero
Affiliation:
[email protected], National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado, 80401-3393, United States
Minjoo Larry Lee
Affiliation:
[email protected], Yale University, Electrical Engineering, New Haven, Connecticut, United States
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Abstract

Metamorphic triple-junction solar cells can currently attain efficiencies as high as 41.1%. Using additional junctions could lead to efficiencies above 50%, but require the development of a wide bandgap (2.0-2.2eV) material to act as the top layer. In this work we demonstrate wide bandgap InyGa1-yP grown on GaAsxP1-x via solid source molecular beam epitaxy. Unoptimized tensile GaAsxP1-x buffers grown on GaAs exhibit asymmetric strain relaxation, along with formation of faceted trenches 100-300 nm deep in the [01-1] direction. Smaller grading step size and higher substrate temperatures minimizes the facet trench density and results in symmetric strain relaxation. In comparison, compressively-strained graded GaAsxP1-x buffers on GaP show nearly-complete strain relaxation of the top layers and no evidence of trenches. We subsequently grew InyGa1-yP layers on the GaAsxP1-x buffers. Photoluminescence and transmission electron microscopy measurements show no indication of phase separation or CuPt ordering. Taken in combination with the low threading dislocation densities obtained, MBE-grown InyGa1-yP layers are promising candidates for future use as the top junction of a multi-junction solar cell.

Type
Research Article
Copyright
Copyright © Materials Research Society 2010

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