Low‐Temperature Transport in Crystalline Ge1Sb2Te4

Disorder and its reduction upon annealing play a crucial role in understanding the electrical transport in the crystalline phase-change material Ge1Sb2Te4. Previous studies focus either on the impact of disorder at moderate temperatures or on the low-temperature properties of crystalline films with a low degree of disorder. The present investigation describes and discusses the impact of pronounced disorder on charge transport at low temperatures. The present data reveal the existence of a metal-to-insulator transition (MIT), where upon increasing order the zero-temperature limit of conductivity changes from zero (insulator) to nonzero values (metal). The position of the MIT is determined with respect to the control parameter, i.e., the disorder, which is modified through the annealing conditions. Disorder is shown to localize carriers for an exceptionally large density of states. In the most disordered films, variable range hopping is observed, enabling the determination of the localization length. At the lowest temperatures studied, deviations from Mott variable range hopping are observed, which can be explained by a transition to Efros–Shklovskii hopping due to the presence of a soft Coulomb gap.