The Study Of The Metastable Phase Structure And Electrical Property Of GeSb₂Te₄

Nonvolatile GeSbTe-based phase change memories have been widely applied in industry due to the excellent properties of phase change materials?PCMs?.The GeSbTe PCMs undergo rapid phase transition between the crystalline phase?low resistance state?and the amorphous phase?high resistance state?.The messages are recorded based on the resistivity difference between crystalline and amorphous phases.The structures of crystalline GeSbTe have not been revealed unambiguously.GeSb₂Te₄ thin films were prepared using DC/magnetron sputtering techniques.The structures of the films were investigated based on the advanced transmission electron microscopy,which includes diffraction,radial distribution function,high-resolution microscopic imaging and simulation techniques.And the corresponding electrical properties of the films were studied by Hall effect measurement.The main results are listed as followings:1.Radio frequency?RF?magnetron sputtered GeSb₂Te₄ films?100W?were annealed at 150?,200?,and 250?for 60 minutes,respectively.The electron diffraction patterns reveal that after annealing all the samples crystallize into cubic phases.However,based on the analysis of the radial distribution function,we found that the cubic phase at 250?is very similar with the spinel structure while those at150?and 200?are identified to be the rocksalt structure.2.We further investigate the structure evolutions of GeSb₂Te₄ films prepared at two different powers?100W and 40W?in the annealing process.The GeSb₂Te₄structures were revealed by the electron diffraction,the radial distribution function,the high-resolution electron microscope and corresponding simulation techniques.The GeSb₂Te₄ film deposited at 100W crystallized into spinel structure after annealing at 250?for 60 min.However,the films deposited at 40W remained to be hexagonal phase in the annealing process.The different structural evolutions in the aging process for GeSb₂Te₄ films prepared at different powers can be attributed to the pristine structural difference between as-deposited films.Compared with the film deposited at40W,the Ge Sb₂Te₄ film prepared at 100W may have more tetrahedral“seeds”in pristine amorphous structure.This could be the reason for the 100W deposited film to crystallize into the spinel structure after annealing.3.The atomic force microscopy reveals that the sputtering power has great impact on the quality of the as-deposited film.Moreover,the Hall effect measurement reveals that the sputtering power also affect the conductivity type of the films.The conduction of the DC sputtered GeSb₂Te₄ films is hybridized by electron conduction and hole conduction.The percentage of n-type conduction of as-deposited film increases first with the sputtering power increasing and then decreases at 80W.For the metastable phase,with the increase of the sputtering power,the percentage of n-type conductivity decreases first and then increases at 60W.While for the stable phase,the percentage of p-type conductivity coarsely increases with the sputtering power increaseing.After the metastable cubic,the films?RF sputtering?of the conductivity type is completely converted to hole conduction.