Spectroscopic investigation on phase transitions for Ge 2Sb 2Te 5 in a wide photon energy and high temperature region

Y. K. Seo, J. S. Chung, Y. S. Lee, E. J. Choi, B. Cheong

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


We investigated the electronic properties of phase-change material Ge 2Sb 2Te 5 (GST) films using spectroscopic ellipsometry in a wide photon energy and high temperature region. Apart from the charge carrier response, the totality of optical conductivity spectra for three phases of GST films, i.e., amorphous (AM), face-centered-cubic (FCC), and hexagonal (HEX), is quite similar, composed of two interband transitions in visible and UV regions. From optical analysis in a wide photon energy region up to 8.7 eV, we found that the intensity as well as the position of the interband transition in the visible region changes significantly as the phase of GST films turns from the amorphous to the crystalline phase, which is consistent with previous theoretical studies. In high temperature measurements above room temperature for the three phases of GST films, we found that the change of optical response for the AM phase of GST film occurs abruptly through two successive phase transitions near 150°C and 270°C, while the optical spectra of the FCC phase shows a change only near 270°C. In contrast to the two above-mentioned cases, a slight change in optical spectra is observed for the HEX phase with the increasing temperature. From the measured optical spectra, we derived the temperature dependence of optical bandgap for the three phases, which are closely correlated to the change of the transport property for the GST films.

Original languageEnglish
Pages (from-to)3458-3463
Number of pages6
JournalThin Solid Films
Issue number9
StatePublished - 29 Feb 2012


  • Amorphous phase
  • Crystalline phase
  • Ellipsometry
  • Ge Sb Te (GST)
  • Optical constants


Dive into the research topics of 'Spectroscopic investigation on phase transitions for Ge 2Sb 2Te 5 in a wide photon energy and high temperature region'. Together they form a unique fingerprint.

Cite this