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Significant Compositional Changes and Formation of a Ga-O Phase after Oxygen-annealing of Ga-rich CuGaSe2 Films

Published online by Cambridge University Press:  21 March 2011

Akihiko Nishio ,
Akimasa Yamada ,
Paul. J. Fons ,
Ralf Hunger ,
Koji Matsubara ,
Kakuya Iwata ,
Shigeru Niki  and
Hisayuki Nakanishi
Akihiko Nishio
Affiliation:
Science Univ. of Tokyo, Faculty of Science and Technology, Noda, Chiba, Japan
Akimasa Yamada
Affiliation:
National Institute of Advanced Industrial Science and Technology, Energy Electronics Institute, Thin Film Solar Cells Group, Tsukuba, Ibaraki, Japan
Paul. J. Fons
Affiliation:
National Institute of Advanced Industrial Science and Technology, Energy Electronics Institute, Thin Film Solar Cells Group, Tsukuba, Ibaraki, Japan
Ralf Hunger
Affiliation:
National Institute of Advanced Industrial Science and Technology, Energy Electronics Institute, Thin Film Solar Cells Group, Tsukuba, Ibaraki, Japan
Koji Matsubara
Affiliation:
National Institute of Advanced Industrial Science and Technology, Energy Electronics Institute, Thin Film Solar Cells Group, Tsukuba, Ibaraki, Japan
Kakuya Iwata
Affiliation:
National Institute of Advanced Industrial Science and Technology, Energy Electronics Institute, Thin Film Solar Cells Group, Tsukuba, Ibaraki, Japan
Shigeru Niki
Affiliation:
National Institute of Advanced Industrial Science and Technology, Energy Electronics Institute, Thin Film Solar Cells Group, Tsukuba, Ibaraki, Japan
Hisayuki Nakanishi
Affiliation:
Science Univ. of Tokyo, Faculty of Science and Technology, Noda, Chiba, Japan
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Abstract

CuGaSe2 (CGS) is a promising material for high efficiency thin film solar cells though predicted device performance has not been realized. Understanding the difference in the chemical nature between CuInSe2 (CIS) and CGS is critical for improving Cu (In, Ga) Se2 solar cells with high Ga concentrations. In this work, we have investigated the effects of oxygen-annealing on Ga-rich CGS epitaxial films focusing on compositional changes and secondary phase formations. The photoluminescence (PL) spectrum of Ga-rich films after oxygen-annealing was observed to always change into a spectrum characteristic of CGS grown under Cu-excess conditions. Electron probe micro-analysis (EPMA) measurements indicate the formation of Ga-O after oxygen-annealing. Selective etching of the Ga-O phase showed the composition of the CGS phase became close to stoichiometric. The oxygen-annealed films showed multiple pits ∼ 100 nm in depth and ∼ 2.5 μm in width. The Ga-O phase is founded in a layer formed on the surface of the CGS phase and in a columnar form rising from the bottom of the pits to the film/substrate interface. The above results suggest that excess Ga in Ga-rich CGS tends to react with oxygen to form Ga-O, thus the composition of the remaining CGS approaches stoichiometry consistent with the changes observed in PL.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 668: Symposium H – II-IV Compound Semiconductor Photovoltaic Materials , 2001 , H5.7
Copyright
Copyright © Materials Research Society 2001

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References

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