Influence of the additive Ag for crystallization of amorphous Ge–Sb–Te thin films

Abstract

We have investigated the optical and amorphous-to-crystalline transition properties in four-types of chalcogenide thin films; Ge 2Sb 2Te 5, Ge 8Sb 2Te 11, Ag–Ge 2Sb 2Te 5 and Ag–Ge 8Sb 2Te 11. Crystallization was caused by nano-pulse illumination ( λ = 658 nm) with power ( P) of 1–17 mW and pulse duration ( t) of 10–460 ns, and the morphologies of crystallized spots were observed by SEM and microscope. It was found that the crystallized spot nearby linearly increases in size with increasing the illuminating energy ( E = P ∙ t) and eventually ablated out by over illumination. Changes in the optical transmittance of as-deposited and annealed films were measured using a UV–vis–IR spectrophotometer. In addition, a speed of amorphous-to-crystalline transition was evaluated by detecting the reflection response signals for the nano-pulse scanning. Conclusively, the Ge 8Sb 2Te 11 film has a faster crystallization speed than the Ge 2Sb 2Te 5 film despite its higher crystallization temperature. The crystallization speed was largely improved by adding Ag in Ge 2Sb 2Te 5 film but not in Ge 8Sb 2Te 11 film. To explain these results, we considered a heat confinement by electron hopping.