5248
Ahmed Ramzy Mohamed Wassel
Preparation, Characterization and Study Some Physical Properties of (Ge4Sb4TeX) Thin Films
Preparation, Characterization and Study Some Physical Properties of (Ge4Sb4TeX) Thin Films
The advantages of chalcogenide phase change materials include the high data storage density, high operational speed, excellent scalability to nanoscale cell size and lower consumption as phase random access memory (PRAM) cell. The compound with chemical composition of Ge4Sb4TeX (where X=6, 8, and 10 at. %) was prepared from high purity constituent of element by melt quench technique. The vacuum thermal evaporation technique is used to deposit thin films of these materials onto glass substrate. The structures of thin films for three compositions are investigated by x-ray diffraction patterns for as deposited and annealed films from 200oC to 350oC. As deposited films for three compositions are amorphous phase, after the annealing which indicates the existence of two crystalline phases face centered cubic (FCC) and hexagonal (hex) phase.The optical (UV-visible) transmission and reflection spectra for as deposited and annealed films were measured in the range (500-2500 nm). The optical transmission and reflectance were measured to calculate the direct and indirect energy gap. The direct and indirect energy gaps were affected by the concentration of tellurium and the annealing temperature of GST system. High resolution transmission electron microscope (HRTEM) confirms the crystallization through electron diffraction pattern. The electron diffraction patterns confirm the existence of the crystalline phases of GST. The lattice pattern indicates the shape of crystals and the lattice plane of the phase formed due to annealing from 200oC to 350oC. The electrical resistivity and conductivity is measured in temperature range from room temperature to 250oC for as deposited and annealed films. The temperature dependence of sheet resistance of GST show drop at 150oC due tothe formation of first phase. Further increase to 200oC show another drop due to the other crystalline phase (hexagonal one). After that calculate the activation energy for as deposited and annealed films from Arrhenius relation, we found that the activation energy decrease with increasing annealed films. The morphology of as deposited and annealed films was studied by field emission scanning electron microscope (FESEM). The surface morphogical features for as deposited show amorphous phase, while the morphogical surface for annealed films indicated that two crystalline phases, the transformation from face centered cubic (FCC) to hexagonal (hex) phase. The results obtained through the thesis indicated that (Ge-Sb-Te) is a very good for application in the field of optical memory devices.
2016
Ph.d
Ain Shams
Science