High transmittance contrast in amorphous to hexagonal phase of Ge_2Sb_2Te_5: Reversible NIR-window

摘要

Ge_2Sb_2Te_5 (GST) is one of the best phase change materials because of its splendid set of properties, viz., high thermal stability, fast crystallization speed, good endurance, scalability, and reliability. Phase transition [amorphous → face centered cubic (fcc) → hexagonal close packed (hep)] of GST thin films with annealing was studied using X-ray diffraction. Thin films in amorphous, fee, and hep phases are highly, medium, and negligible transparent in the near infra-red region, respectively. The optical transmission in amorphous, fee, and hep phases is ～92%, ～46%, and ～2%, respectively, at the wavelength of 2740 nm. At 2740 nm, a high transmission contrast (～90%) is observed with phase transition from the amorphous to hep phase. By utilizing large transmission contrast, it is demonstrated that GST can be availed as a potential candidate for reversible near infra-red-window. The sharp change in optical transmission with phase transition can be understood from the change in density of states in the valence band.