Singh, Palwinder and Singh, A. P. and Sharma, Jeewan and Kumar, Akshay and Mishra, Monu and Gupta, Govind and Thakur, Anup
(2018)
Reduction of Rocksalt Phase in Ag-Doped Ge2Sb2Te5: A Potential Material for Reversible Near-Infrared Window.
Physical Review Applied , 10 (5).
054070-054077.
ISSN 2331-7019
Abstract
hase-change materials are attracting much attention in the scientific and engineering communities owing to their applications and underlying basic phenomena. Ge2Sb2Te5 is reversible-phase-change material (amorphous to crystalline and vice versa) that is used for optical data storage and phase-change random-access memory and has recently been explored for use as a reversible near-infrared (NIR) window [Singh et al., Appl. Phys. Lett. 111, 261102 (2017)]. For a reversible NIR window, large transmission contrast between two phases and low phase-transition temperature are required to reduce the power consumption. In the present work, phase transition in thermally deposited (Ge2Sb2Te5)(100-x)Ag-x (x = 0, 1, 3, 5, and 10) thin films is achieved by vacuum thermal annealing. Transmission sharply decreases with phase transition in the NIR region. Ge2Sb2Te5 shows large transmission contrast (more than 50%) in the wavelength range from 1600 to 3200 nm with phase transition from an amorphous to a hexagonal-close-packed structure at 260 degrees C. In (Ge2Sb2Te5)(90)Ag-10 thin films, a similar transmission contrast is achieved at a comparatively lower temperature (160 degrees C) due to reduction of the rocksalt phase. Distortion of the host lattice with addition of 10% Ag is confirmed from the drastic change in the density of states in the valence band and the shift in core-level (3d) spectra of Ag, Sb, and Te. This distortion enables a hexagonal-close-packed phase in (Ge2Sb2Te5)(90)Ag-10 thin films to be obtained at 160 degrees C. (Ge2Sb2Te5)(90)Ag-10 could be a potential candidate for a reversible NIR window as it requires less power to achieve phase transition and high transmission contrast.
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