Ge2Sb2Te5 films were deposited by RF magnetron sputtering on Si (100)/SiO2 substrates. O+ ion was implanted into Ge2Sb2Te5 films. It is indicated that the structure of crystalline Ge2Sb2Te5-O annealed at 250°C is still identified as a FCC structure and the lattice parameter increases with the increasing oxygen implant dose. However, phase separation takes place when annealing temperature is 450°C. Oxygen implantation has great effect on the resistance of Ge2Sb2Te5 film. Due to oxygen doping, the resistance of Ge2Sb2Te5 film decreases when annealing temperature is lower than 300°C because the FCC unit cell was distorted by oxygen atom occupying the tetrahedral interstitial site and the defects were increased, which results in larger number of current carrier. However, resistance of Ge2Sb2Te5 film increases when annealing temperature is higher than 340°C, which may be caused by phase separation and current carrier being scattered by crystallite boundary.
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