Optical and Electrical Properties of Phase Change Materials


Optical and electrical properties of the phase change material Ge2Sb2Te5 are reviewed for its three phases. Implications of these data for the energy distribution of the density of electron states in the vicinity of the band edges are described. Near-band edge optical data obtained from ellipsometry and optical absorption spectra have been fitted with dispersion equations to determine values of ∼ 0.7 eV for the optical bandgap of the amorphous phase, and ∼ 0.5 eV for the highly conducting fcc and hexagonal phases. Infrared absorption spectra exhibit the effects of free carrier absorption in both crystalline phases. Conductivity at ∼ 300 K is dominated by holes in all three phases; hole concentrations and mobilities are 1020 cm−3 and ∼ 30 cm2/V-s in hexagonal, and 1020 cm-3 and ∼ 1 cm2/V-s in fcc. Temperature dependence of the sheet resistance of thin film Ge2Sb2Te5 documents the dramatic decreases in electrical resistance at the amorphous-to-fcc and fcc-to-hexagonal phase transitions. Comparison of the temperature dependence of the electrical properties in each of the three phases of Ge2Sb2Te5 provides additional insights concerning their conduction mechanisms.


Optical Bandgap Sheet Resistance Optical Constant Phase Change Material Hole Concentration 


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© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.Department of Materials Science and the Coordinated Science LaboratoryUniversity of Illinois at Urbana-ChampaignUrbanaUSA
  2. 2.Dept. Head for Administrative and Instructional Affairs, Electrical and Computer Engineering DepartmentUniversity of Illinois at Urbana-Champaign, 153 Everitt LaboratoryUrbanaUSA

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