Abstract
Phase change materials such as pseudobinary GeTe-Sb2Te3 (GST) alloys are an essential part of existing and emerging technologies. Here, we investigate the electrical and optical properties of epitaxial phase change materials: α-GeTe, Ge2Sb2Te5 (GST225), and Sb2Te3. Temperature-dependent Hall measurements reveal a reduction of the hole concentration with increasing temperature in Sb2Te3 that is attributed to lattice expansion, resulting in a non-linear increase of the resistivity that is also observed in GST225. Fourier transform infrared spectroscopy at room temperature demonstrates the presence of electronic states within the energy gap for α-GeTe and GST225. We conclude that these electronic states are due to vacancy clusters inside these two materials. The obtained results shed new light on the fundamental properties of phase change materials such as the high dielectric constant and persistent photoconductivity and have the potential to be included in device simulations.
Highlights
Phase change materials (PCMs) such as GeTe-Sb2Te3 (GST) alloys[1] are extensively used and investigated for their application as a storage medium in optical discs and in phase change random access memory[2,3]
This can be attributed to the close to perfect out-of-plane alignment of epitaxial films or an improvement of the crystalline quality. This indicates that the functional properties of optical devices based on GST225 can be enhanced by using epitaxial or textured GST225, because these devices commonly rely polycrystalline GST225 with a lower real part of the refractive index. The observation that both the hole concentration and the hole mobility of α-GeTe and Sb2Te3 change with temperature suggests that this should occur for GST225
This is important for the modelling of phase change random access memory cells, because the melting of GST225 is due to Joule heating and depends on the electrical resistance
Summary
The observation that both the hole concentration and the hole mobility of α-GeTe and Sb2Te3 change with temperature suggests that this should occur for GST225 This is important for the modelling of phase change random access memory cells, because the melting of GST225 is due to Joule heating and depends on the electrical resistance. The finding that the hole concentration changes with the lattice volume is relevant for applications, because the expansion of PCMs is restricted in typical devices. This can influence the hole concentration and the resistance. Further improvements of the quality of epitaxial PCMs such as a reduction of the hole concentration might improve the insights into the fundamental properties of this fascinating material class
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