Investigation of the structural and optical properties of Ge-doped SbTe films with various Sb:Te ratios

Title
Investigation of the structural and optical properties of Ge-doped SbTe films with various Sb:Te ratios
Authors
강태동Andrei Sirenko박준우이현석이수연정증현정병기이호선
Keywords
phase change memory; Ge-doped SbTe; optical; structural
Issue Date
2011-03
Publisher
Journal of the Electrochemical Society
Citation
VOL 158, NO 3, H249-H254
Abstract
In this study, we investigated the structural and optical properties of Ge-doped SbTe (Ge–ST) thin films with three differing compositions: Ge0.06Sb0.77Te0.17 (Ge–STH), Ge0.05Sb0.70Te0.25 (Ge–STM), and Ge0.05Sb0.64Te0.31 (Ge–STL), grown on Si substrate by radio-frequency sputtering method. The films were annealed at 250°C for crystallization and their crystal structures were examined by X-ray diffraction. Compared to the X-ray diffraction spectra of the undoped SbTe, the Ge–ST thin films had a hexagonal structure with large stacking periods. Using Raman spectroscopy, we investigated the shift of the phonon mode frequencies (A1g and Eg) of the films with varying Sb:Te ratios. We compared the dependence of the phonon frequencies of Ge–ST on the Sb content to those of the corresponding undoped SbTe. The composition dependence of the A1g phonon frequency could be explained in terms of the linear extrapolation of Sb and Sb2Te3 crystals. By using spectroscopic ellipsometry, we measured the dielectric function of the thin films in the near-IR, visible, and ultraviolet spectral regions. The optical energy gaps and bandgaps of the amorphous and crystalline phases, respectively, were determined using linear extrapolation of the absorption coefficient. The optical gap energies of the amorphous Ge–ST films were determined to be about 0.5–0.6 eV, whereas the indirect bandgap energies of the crystalline films shrank substantially to about 0.15–0.2 eV.
URI
http://pubs.kist.re.kr/handle/201004/39446
ISSN
0013-4651
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