Crystallization behavior of amorphous Alx(Ge2Sb2Te5)1−x thin films

Abstract

Crystallization properties of thermally deposited amorphous Alx(Ge2Sb2Te5)1−x (x=0.06 and 0.10) films were investigated. The crystallization was performed by both macroscopic thermal annealing and nanopulse laser illumination (λ=658 nm and beam diameter <2 μm). The Al0.10(Ge2Sb2Te5)0.90 film exhibited a very stable one-step phase transition from amorphous→face-centered cubic (fcc) in the annealing temperature range of 100–300 °C. The Al0.10(Ge2Sb2Te5)0.90 film had a higher sheet resistances (RS) in both the amorphous and crystalline phases compared to the Ge2Sb2Te5 film, resulting in lower set and reset programming currents in the phase-change random-access memory. The crystallization speed (v) of the amorphous films was quantitatively and qualitatively evaluated through the analysis of the surface images and the nanopulse reflection-response curves. Conclusively, the Al atom added into Ge2Sb2Te5 serves as a center for suppression of the fcc-to-hexagonal phase transition and the v-value was largely improved by the proper addition of Al, e.g., v[Al0.10(Ge2Sb2Te5)0.90]>v[Ge2Sb2Te5]. Additionally, the improved v was believed to result from improvements in both the nucleation and growth processes.