Study of structural and electrical properties of phase-change materials Ge1Sb2Te4 and Ge2Sb2Te5 thin films

The Ge1Sb2Te4 and Ge2Sb2Te5 thin films were deposited on quartz and silicon substrates by radio frequency magnetron sputtering from Ge1Sb2Te4 and Ge2Sb2Te5alloy targets. Structure properties and electrical transport characteristics of Ge1Sb2Te4 and Ge2Sb2Te5 thin films were studied and compared. X-ray diffraction spectra and atomic force microscopic images were used to characterize the structure of Ge1Sb2Te4 and Ge2Sb2Te5before and after thermal annealing. With increasing annealing temperature, Ge1Sb2Te4crystallized gradually and transformed to polycrystalline state from the amorphous state. Surface of Ge1Sb2Te4 thin films was uniform nanoparticles with roughness less than 10 nm. After thermal annealing, Ge2Sb2Te5 also transformed to polycrystalline state from amorphous state, but its surface morphology did not change significantly compared with the as-deposited film. Results of Hall effect measurement indicated the carrier concentrations of both the as-deposited and annealed films of Ge1Sb2Te4 were three orders of magnitude larger than those of Ge2Sb2Te5. From the above results, we conclude that Ge1Sb2Te4 tends to be more conductive than Ge2Sb2Te5 owing to the larger carrier concentration. Results of resistance versus time measurements under isothermal condition suggested Ge2Sb2Te5is more thermally stable and better fit for data storage than Ge1Sb2Te4.