Effects of Grain Boundaries on THz Conductivity in the Crystalline States of Ge2Sb2Te5 Phase‐Change Materials: Correlation with DC Loss

Herein, in situ temperature-dependent THz and DC conductivity measurements in the crystalline states of Ge2Sb2Te5(GST225) are performed at relatively high temperatures (>300 K). As observed in many nanomaterials, a non-Drude type of THz conductivity is found in the crystalline state of phase-change (PC) materials. Both the intra- and intergrain effects can be separated in the THz and DC conductivity. It is shown that grain boundaries significantly affect the THz and DC conductivities of the crystalline phase (distorted rock salt structure). The experimentally observed DC Hall mobility is different from the intragrain mobility extracted from the THz conductivity, suggesting that a series sequence of intra- and intergrain transport mechanisms controls the electronic transport in the crystalline state of GST225.