Crystallization of amorphous Ge ₂ Sb ₂ Te ₅ films induced by an ultraviolet laser

The laser wavelength plays an important role in achieving high density in optical storage. Previous studies on the phase transition were mainly focused on the range from infrared to visible waveband. In this work, crystallization of amorphous Ge ₂ Sb ₂ Te ₅ thin film induced by an ultraviolet laser with the wavelength of 248 nm was investigated. The crystallization behavior of Ge ₂ Sb ₂ Te ₅ thin films was analyzed using X-ray diffraction, atomic force microscopy, Raman scattering and scanning electron microscope. Based on the X-ray diffraction pattern results, the phase transition from the amorphous Ge ₂ Sb ₂ Te ₅ to the face-centered cubic crystallized Ge ₂ Sb ₂ Te ₅ was obtained with the laser fluence in the range of 24.4-66.6 mJ/cm ² . Atomic force microscopy images showed that the inhomogeneous crystalline structure with the grain size ranging from tens of nanometer to 250 nm was produced in spite of the lower laser fluence of 24.4 mJ/cm ² . This structure can be attributed to the ultrafast violet laser radiance. A new peak at 140 cm ^-1 caused by the segregation of Te crystalline was possibly due to the higher photon energy absorbed by the ultraviolet laser radiance. This work is of significance for the optical storage in developing new applications by ultraviolet laser.