Seo, Y. K. Chung, J-S Lee, Y. S. Choi, E. J. Cheong, B. 2024-01-20T15:30:50Z 2024-01-20T15:30:50Z 2021-09-04 2012-02-29 0040-6090 https://pubs.kist.re.kr/handle/201004/129521 We investigated the electronic properties of phase-change material Ge2Sb2Te5 (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 degrees C and 270 degrees C, while the optical spectra of the FCC phase shows a change only near 270 degrees 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. (C) 2011 Elsevier B.V. All rights reserved. English ELSEVIER SCIENCE SA OPTICAL-PROPERTIES DEPENDENCE GAP GE SB Spectroscopic investigation on phase transitions for Ge2Sb2Te5 in a wide photon energy and high temperature region Article 10.1016/j.tsf.2011.12.043 1 THIN SOLID FILMS, v.520, no.9, pp.3458 - 3463 THIN SOLID FILMS 520 9 3458 3463 scie scopus 000301627100007 2-s2.0-84862812879 Materials Science, Multidisciplinary Materials Science, Coatings & Films Physics, Applied Physics, Condensed Matter Materials Science Physics Article OPTICAL-PROPERTIES DEPENDENCE GAP GE SB Ge2Sb2Te5 (GST) Optical constants Ellipsometry Amorphous phase Crystalline phase