Phase separation of a Ge2Sb2Te5 alloy in the transition from an amorphous structure to crystalline structures

Changes in the structural and electrical properties of a Ge2Sb2Te5 alloy thin film induced by phase transition were investigated using various analytical techniques. X-ray diffraction and scanning photoelectron microscopy showed that the phase separation occurred in a local. area of the film during a phase transition when the amorphous structure was being transformed into crystalline structures. It was found that the heterogeneous distribution of Sb atoms that diffused during the phase transition accompanied the phase separation. Atomic force microscopy was used to examine the changes in surface morphology and roughness. The electrical conductance of the film was dramatically improved after the phase transition from an amorphous structure to crystalline structures as evidenced by the sheet resistance measurements. The sheet resistance changed from similar to 10(9) to similar to 10(2) Omega/sq. during the phase transition. Differential scanning calorimetry was used to determine the exact phase transition temperature (160-170 degrees C) and the effective activation energy for the phase transition (2.5 +/- 0.11 eV) on the basis of Kissinger's equation. (c) 2006 American Vacuum Society.