Photo-oxidation and the absence of photodarkening in Ge2Sb 2Te5 phase change material

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, Heng Li, P. Craig Taylor

Research output: Contribution to journalConference articlepeer-review


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 the amorphous phase. Many chalcogenide glasses 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 GexSb 20-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 actually the result of photo-oxidation. The oxide has lower values of (n, k) than Ge2Sb2Te 5, and can be etched by hydrofluoric acid or water. Our observation of negligible photodarkening is consistent with previous work 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.

Original languageEnglish (US)
Pages (from-to)113-118
Number of pages6
JournalMaterials Research Society Symposium Proceedings
StatePublished - 2006
Event2006 MRS Spring Meeting - San Francisco, CA, United States
Duration: Apr 17 2006Apr 21 2006

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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