Amorphous-to-crystalline phase transformation in (GeTe)x(Sb2Te3) (x = 0.5, 1, 2, 8) thin films

In this work, several experimental methods were used to evaluate the phase transformation characteristics of Ge-Sb-Te pseudobinary thin films that were comprehensively utilized as phase change materials. Except for Ge8Sb2Te11 (x = 8), the phase transition of the (GeTe)x(Sb2Te3) (x = 0.5, 1, 2) thin films from the amorphous to the hexagonal structure via the fcc structure was confirmed by X-ray diffraction the measurements. Additionally, the X-ray photoelectron spectra analysis revealed that the Ge-Te bond was weakened for Ge2Sb2Te5 (x = 2) and all of bonds were strengthened for Ge8Sb2Te11 (x = 8) during the amorphous to crystalline transition. The optical energy gaps (EOP) were around 0.71 and 0.50 eV, and the slopes of the absorption in the extended region (B) were ∼5.1 × 105 and ∼10 × 105 cm−1·V−1 for the amorphous and the fcc crystalline structures, respectively. Finally, the speed of the amorphous-to-crystalline phase transition for the (GeTe)x(Sb2Te3) (x = 0.5, 1, 2) films was characterized by using a nano-pulse scanner with a 658-nm laser diode (power: 1 ∼ 17 mW, pulse duration: 10 ∼ 460 ns).