The microstructure and electrical and optical properties of Ge-Cu-Te phase-change thin films

We investigated the microstructure and texture of completely crystalline Ge-Cu-Te thin films, focusing on the grain orientation, grain boundary character distribution and morphology, and their correlation with electrical and optical behaviors, as phase-change materials for application in phase change memory (PCM). In this study, the preferred {111} orientation was observed in thin films annealed at 300 degrees C, which is favorable for improving carrier mobility. As the annealing temperature increases to 400 degrees C, the grain orientation evolves into a random distribution, which is beneficial for improving optical reflectivity. The corresponding orientation evolution mechanism involves the effects of work function, surface energy, and different stress states during annealing. In addition, a high fraction of high angle grain boundaries mixed with a fraction of 60 degrees 111 and 30 degrees 110 grain boundaries is prevalent in the crystalline thin films, which is related to the great thermal stress and orientation randomization in the crystalline thin films. For completely crystallized thin films, the cross-section grain growth, accompanying numerous stacking faults and dislocations, has already spanned the entire thin films thickness direction. This work shows that the grain orientation of phase change materials can be highly impacted by thermal circumstances, which is expected to shed light on the phase-change thin film growth. The grain orientation of Ge-Cu-Te films evolves from the {111} texture with favorable carrier mobility into a random distribution with improved optical reflectivity as the annealing temperature increases.