Shortening Nucleation Time to Enable Ultrafast Phase Transition in Zn₁Sb₇Te₁₂ Pseudo-Binary Alloy

Zn₁Sb₇Te₁₂ thin films have been deposited by magnetron co-sputtering of ZnTe and Sb₂Te₃ targets. The microstructure, phase-change speed, optical cycling stability, and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give a clear evidence of the coexistence of trigonal Sb₂Te₃ and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy. The formation of both phases increases the initial nucleation sites, leading to the rapid phase-change speed in the Zn₁Sb₇Te₁₂ film. The film has a minimum crystallization time of ∼3 ns at 70 mW with almost no incubation period for the formation of critical nuclei compared to Ge₂Sb₂Te₅ and other Zn-based films. Moreover, the complete crystallization of Zn₁Sb₇Te₁₂ thin films is achieved within 10 ns. The ultrafast two-dimensional nucleation and crystal growth speed in Zn₁Sb₇Te₁₂ obtained from the laser-irradiated system is almost 7 times faster compared to that in Ge₂Sb₂Te₅ film. Controlling the crystallization process through doping ZnTe into Sb₂Te₃ is thus promising for the development of high-speed optical switching technology.