Comments on the electronic transport mechanisms in the crystalline state of Ge—Sb—Te phase-change materials

• Published in: Physics of complex systems Vol. 2; no. 2; pp. 74 - 80
• Main Authors: Shimakawa, Koichi, Jeronimo Freitas, Ruben
• Format: Journal Article
• Language: English
• Published: Herzen State Pedagogical University of Russia 01.06.2021
• Subjects: crystalline phase; degenerate semiconductor; electronic transport; Ge—Sb—Te phase-change materials; grain boundary; metal-insulator transition
• ISSN: 2687-153X; 2687-153X
• DOI: 10.33910/2687-153X-2021-2-2-74-80

It is known that phase-change materials, such as Ge–Sb—Te ternary system, are promising resistive non-volatile random-access memory applications with ultra-rapid reversible transformations between the crystalline and amorphous phases. This class of electronic transition is categorized to be the metal-insulator transition (MIT). The Anderson-type MIT has been discussed extensively in phase-change materials (PCMs) and isothermal annealing of amorphous PCMs (a-PCMs) which, above a certain temperature, leads to the metallic (crystalline) phase. In the insulator regime near the MI transition, Mott-type variable-range hopping (VRH) and/or Efros-Shkolvskii hopping (ESH) at low temperatures below 20 K (and down to 1 K) in Ge1Sb2Te4 (GST124) have been discussed extensively, however, we criticize the above argument through a detailed discussion of physical parameters that support the VRH mechanism. It is not clear whether or not the density-of-states (DOS) near the Fermi level is localized (like the Fermi glass) in the crystalline phase. It is also suggested that grain boundaries are expected to interfere with the electronic transport in the crystalline state. We should take into account the grain boundary effects on the electronic transport in the crystalline phase of Ge—Sb—Te system.