Tungsten (W) doping effects on Ge2Sb2Te5 (GSTW) phase change films with different concentrations (3.2, 7.1, and 10.8%) have been investigated by variable-temperature spectroscopic ellipsometry. The dielectric functions from 210 K to 660 K have been evaluated with the aid of Tauc-Lorentz and Drude dispersion models. The analysis of Tauc gap energy (Eg) and partial spectral weight integral reveal the correlation between optical properties and local structural change. The order degree increment and chemical bond change from covalent to resonant should be responsible for band gap narrowing and electronic transition enhancement during the phase change process. It is found that the elevated crystalline temperature for GSTW can be related to improved disorder degree. Furthermore, the shrinkage of Eg for GSTW should be attributed to the enhanced metallicity compared with undoped GST.
Articles you may be interested inBroadband inelastic light scattering study on relaxor ferroelectric Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals Electrocaloric properties in relaxor ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 system Phase transition behaviors in relaxor ferroelectric [001]-poled Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals studied by Brillouin light scattering and dielectric spectroscopies Optical properties and phase transitions of Pb(In 1=2 Nb 1=2 )O 3 -Pb(Mg 1=3 Nb 2=3 )O 3 -PbTiO 3 (PIN-PMN-PT) crystals near morphotropic phase boundary (MPB) have been investigated by temperature dependent transmittance and reflectance spectra. Three critical point energies E g ¼ 3.17-3.18 eV, E a ¼ 3.41-3.61 eV, and E b ¼ 4.74-4.81 eV can be assigned to the transitions from oxygen 2p to titanium d, niobium d, and lead 6p states, respectively. They show narrowing trends with increasing temperature, which can be caused by thermal expansion of the lattice and electron-phonon interaction. Deviation from the linear behaviors can be observed from E a and E b versus PT concentration, indicating a complex multiphase structure near MPB region. V C 2014 AIP Publishing LLC. [http://dx.
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