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Study of Band Alignment at CBD-CdS/Cu(In1-xGax)Se2 (x = 0.2 - 1.0) Interfaces by Photoemission and Inverse Photoemission Spectroscopy

Published online by Cambridge University Press:  01 February 2011

Shimpei Teshima
Affiliation:
bt202049@ms.kagoshima-u.ac.jp, Kagoshima University, Nano-structure and Advanced Materials, 1-21-40, Korimoto, Kagoshima, 890-0065, Japan
Hirotake Kashiwabara
Affiliation:
ee01016@h13.eee.kagoshima-u.ac.jp, Kagoshima University, Nano-structure and Advanced Materials, 1-21-40, Korimoto, Kagoshima, 890-0065, Japan
Keimei Masamoto
Affiliation:
bt202075@ms.kagoshima-u.ac.jp, Kagoshima University, Nano-structure and Advanced Materials, 1-21-40, Korimoto, Kagoshima, 890-0065, Japan
Kazuya Kikunaga
Affiliation:
ee01023@h13.eee.kagoshima-u.ac.jp, Kagoshima University, Nano-structure and Advanced Materials, 1-21-40, Korimoto, Kagoshima, 890-0065, Japan
Kazunori Takeshita
Affiliation:
bt202049@ms.kagoshima-u.ac.jp, Kagoshima University, Nano-structure and Advanced Materials, 1-21-40, Korimoto, Kagoshima, 890-0065, Japan
Tetsuji Okuda
Affiliation:
okuda@eee.kagoshima-u.ac.jp, Kagoshima University, Nano-structure and Advanced Materials, 1-21-40, Korimoto, Kagoshima, 890-0065, Japan
Keiichiro Sakurai
Affiliation:
k-sakurai@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono, Tsukuba, 305-8568, Japan
Shogo Ishizuka
Affiliation:
shogo-ishizuka@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono, Tsukuba, 305-8568, Japan
Akimasa Yamada
Affiliation:
a.yamada@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono, Tsukuba, 305-8568, Japan
Koji Matsubara
Affiliation:
koji.matsubara@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono, Tsukuba, 305-8568, Japan
Shigeru Niki
Affiliation:
shigeru-niki@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono, Tsukuba, 305-8568, Japan
Yukio Yoshimura
Affiliation:
yosiyuki@kagoshima-it.go.jp, Kagoshima Prefectural Institute of Industrial Technology, 1445-1, Oda, Hayato, Kirishima, 899-5105, Japan
Norio Terada
Affiliation:
terada@eee.kagoshima-u.ac.jp, Kagoshima University, Nano-structure and Advanced Materials, 1-21-40, Korimoto, Kagoshima, 890-0065, Japan
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Abstract

Dependence of band alignments at interfaces between CdS by chemical bath deposition and Cu(In1-xGax)Se2 by conventional 3-stage co-evaporation on Ga substitution ratio x from 0.2 to 1.0 has been systematically studied by means of photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES). For the specimens of the In-rich CIGS, conduction band minimum (CBM) by CIGS was lower than that of CdS. Conduction band offset of them was positive about +0.3 ~ +0.4 eV. Almost flat conduction band alignment was realized at x = 0.4 ~ 0.5. On the other hand, at the interfaces over the Ga-rich CIGS, CBM of CIGS was higher than that of CdS, and CBO became negative. The present study reveals that the decrease of CBO with a rise of x presents over the wide rage of x, which results in the sign change of CBO around 0.4 ~ 0.45. In the Ga-rich interfaces, the minimum of band gap energy, which corresponded to energy spacing between CBM of CdS and valence band maximum of CIGS, was almost identical against the change of band gap energy of CIGS. Additionally, local accumulation of oxygen related impurities was observed at the Ga-rich samples, which might cause the local rise of band edges in central region of the interface.

Type
Research Article
Copyright
Copyright © Materials Research Society 2007

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