Electrical and optical properties of epitaxial binary and ternary GeTe-Sb₂Te₃ alloys

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.