Effect of vacuum annealing on structural and electrical properties of germanium telluride thin films

•As-prepared GeTe films deposited at 25 °C were amorphous.•The degree of crystallinity of GeTe films increased when annealing time increased.•The average grain size increased by 60% upon doubling the annealing time.•Upon crystallization, Te-rich tetrahedra formation is favored over Ge-rich tetrahedra. This study investigates the effects of vacuum annealing on the structural and electrical properties of germanium telluride thin films. To this end, GeTe thin films were prepared via DC magnetron sputtering in three sets—as-prepared at 25 °C, as-prepared at 300 °C, and deposited and annealed at 300 °C for different time intervals. Post fabrication, the films were characterized using grazing-incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and four-point probe measurements. The as-prepared films deposited at 25 °C were amorphous, while the remaining film types exhibited crystalline conductivity and comparable sheet-resistance values. However, the observations of this study reveal a gradual increase in the degree of crystallinity and average grain size of the annealed films. The Raman spectroscopy results reveal the increase in film crystallinity to be due to an increase in the concentration of Te-rich tetrahedra at the expense of their Ge-rich equivalents. [Display omitted]