Crystallization properties of melt-quenched Ge-rich GeSbTe thin films for phase change memory applications

The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm−2, a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm−2, only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs.