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Photo-oxidation and the Absence of Photodarkening in Ge2Sb2Te5 Phase Change Material

Published online by Cambridge University Press:  01 February 2011

Bong-Sub Lee ,
Ying Xiao ,
Stephen G. Bishop ,
John R. Abelson ,
Simone Raoux ,
Vaughn R. Deline ,
Min-Ho Kwon ,
Ki-Bum Kim ,
Byung-ki Cheong  and
Heng Li
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Bong-Sub Lee
Affiliation:
blee@uiuc.edu, University of Illinois at Urbana-Champaign, Materials Science and Engineering, 1101 W. Springfield Ave., Rm 1-110, Urbana, IL, 61801, United States, 1-217-244-0332
Ying Xiao
Affiliation:
yxiao2@uiuc.edu, University of Illinois at Urbana-Champaign, Department of Materials Science and Engineering, Urbana, IL, 61801, United States
Stephen G. Bishop
Affiliation:
sgbishop@uiuc.edu, University of Illinois at Urbana-Champaign, Department of Electrical and Computer Engineering, Urbana, IL, 61801, United States
John R. Abelson
Affiliation:
abelson@uiuc.edu, University of Illinois at Urbana-Champaign, Department of Materials Science and Engineering, Urbana, IL, 61801, United States
Simone Raoux
Affiliation:
simone_raoux@almaden.ibm.com, IBM Almaden Research Center, San Jose, CA, 95120, United States
Vaughn R. Deline
Affiliation:
deline@almaden.ibm.com, IBM Almaden Research Center, San Jose, CA, 95120, United States
Min-Ho Kwon
Affiliation:
jb0530@snu.ac.kr, Seoul National University, School of Materials Science and Engineering, Seoul, N/A, 151-742, Korea, Republic of
Ki-Bum Kim
Affiliation:
kibum@snu.ac.kr, Seoul National University, School of Materials Science and Engineering, Seoul, N/A, 151-742, Korea, Republic of
Byung-ki Cheong
Affiliation:
bkcheong@kist.re.kr, Korea Institute of Science and Technology, Thin Film Materials Research Center, Seoul, N/A, 136-791, Korea, Republic of
Heng Li
Affiliation:
hengli@physics.utah.edu, Colorado School of Mines, Physics Department, Golden, Co, 80401, United States
P. Craig Taylor
Affiliation:
pctaylor@mines.edu, Colorado School of Mines, Physics Department, Golden, Co, 80401, United States
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Abstract

Ge2Sb2Te5 is under intense investigation for phase-change memory devices, including rewriteable DVDs where optical illumination is used to switch between the glassy and crystalline states. We investigate the influence of optical irradiation on amorphous phase. Many chalcogenides display photo-oxidation, photodarkening or photo-bleaching, but little has been reported on the Ge-Sb-Te system. Using spectroscopic ellipsometry (SE) and secondary ion mass spectrometry, we determine that the samples have a strong tendency to photo-oxidize; if this is not accounted for, then the analysis of SE data appears to show photodarkening. Other authors recently reported photodarkening in nonstoichiometric GexSb20-xTe80 [Pamukchieva et al., Proc. SPIE 5581, 608 (2004); Pamukchieva et al., J. Optoelectron. Adv. Mater 7, 1277 (2005)], but our analysis suggests that the changes were also the result of photo-oxidation. The oxide has lower value of (n, k) than Ge2Sb2Te5, and can be etched by hydrofluoric acid or water. The photo-oxidation is presumably the result of free carrier generation in the Ge2Sb2Te5. Our observation of negligible photodarkening is consistent with previous works that found less photodarkening in tellurides compared with selenides or sulfides, and that an increase in the mean coordination number, here by Ge addition, further reduces the photodarkening effect.

Keywords

phase transformationoptical propertiesoxidation
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 918: Symposium H – Chalcogenide Alloys for Reconfigurable Electronics , 2006 , 0918-H02-04
Copyright
Copyright © Materials Research Society 2006

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