Structural evolution of Ge ₂Sb ₂Te ₅ films under the 488 nm laser irradiation

Ge ₂Sb ₂Te ₅ films were locally crystallized by a tightly focused laser beam and the structural evolution was studied by Raman scatting. The marks recorded by a broad range of laser power were studied by optical microscope. Raman spectra of films with irradiation power of 0.1 mW and 1 mW were consistent with those of films annealed at 140°C and 400°C, respectively. It reveals that both the cubic and hexagonal crystalline phases have been achieved under the irradiation of 488 nm laser in amorphous Ge ₂Sb ₂Te ₅ films. Specifically, the appearance of a new band of ∼141 cm ^-1 in films with irradiation power larger than 1.25 mW confirms that the over-irradiation causes the segregation of Te crystalline phase in films.