Effects Of Hydrostatic Pressure On The Electrical Properties Of Ge₂Sb₂Te₅

In recent decades, with the rapid development of semiconductor technology, more and more original components are combined into the integrated circuits, which makes the critical dimension of the devices in the chip become much smaller. Now the dimension is close to the limit of physical processes, and further reducing the line width of the devices is very difficult, considering the current technology of photolithography. With the shrinking of devices, the size effects of the materials will show up, and the classical or semi-classical theory can be no longer used to describe the physical properties of the nanoscale devices. At the same time, the sharp increase of the drain current and power consumption easily cause the failure of the devices due to the quantum tunneling effects. Now the semiconductor technology faces with great problems both in theory and technology. So looking for a new generation of storage technology of non-volatile, high storage density, low power and long data retention time has become a pressing task in current development of semiconductor technology. Phase change random access memory (PCRAM), a kind of memory based on the large electrical contrast between the amorphous phase and the crystalline phase of chalcogenide compound materials, has drawn a lot of attention because of the fast speed, high storage density, non-volatile and being compatible with conventional CMOS technology. And it is a potential candidate of next-generation nonvolatile memory devices.In this work, a combination of experiments and first-principles method calculations has been applied to investigate the influence of the hydrostatic pressure on the electrical properties of the phase-change material Ge2Sb2Te5. The main conclusions are summarized as followed:1. The Ge2Sb2Te5 films were prepared by RF magnetron sputtering system, and were identified by using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD). The results determine the characteristics of crystalline Ge2Sb2Te5 materials.2. The temperature-resistance (R-T) properties of the face-centered cubic phase and the hexagonal phase of Ge2Sb2Te5 materials were measured. For both of the two crystalline phases of Ge2Sb2Te5 materials, the resistance decreases with the rise of temperature, which indicates that both of the crystalline phases of Ge2Sb2Te5 materials are semiconductors.3. The dependence of electrical resistance on hydrostatic pressure was measured. It's found that the resistance of cubic Ge2Sb2Te5 reduces continuously and changes about 15.05% when the hydrostatic pressure rises to 0.6 GPa. The band-structure calculations reveals that the electronic band gap decreases with the pressure, which response to the decline of resistivity of cubic Ge2Sb2Te5.4. Experimental and theoretical investigations have been carried out about the influence of the hydrostatic pressure on the electrical properties of the phase change material hexagonal Ge2Sb2Te5. Experimentally, it is found that the resistance of hexagonal Ge2Sb2Te5 declines monotonically with increasing hydrostatic pressure up to 0.7 GPa. Theoretically, the band-structure calculations reveals that the electronic band gap also decreases with the pressure. The hydrostatic pressure increases the conductivity of hexagonal by reducing the electronic band gap. The dEg/dP obtained from theoretical calculations and the dlnR/dP by experimental result are in the same order of magnitude.