Evidence for electronic gap-driven metal-semiconductor transition in phase-change materials

Abstract

Phase-change materials are functionally important materials that can be thermally interconverted between metallic (crystalline) and semiconducting (amorphous) phases on a very short time scale.Although the interconversion appears to involve a change in local atomic coordination numbers, the electronic basis for this process is still unclear. Here, we demonstrate that in a nearly vacancy-free binary GeSb system where we can drive the phase change both thermally and, as we discover, by pressure, the transformation into the amorphous phase is electronic in origin. Correlations between conductivity, total system energy, and local atomic coordination revealed by experiments and long time ab initio simulations show that the structural reorganization into the amorphous state is driven by opening of an energy gap in the electronic density of states. The electronic driving force behind the phase change has the potential to change the interconversion paradigm in this material class.ab initio simulations ͉ structural phase change ͉ electronic phase transitions ͉ ac conductivity

Irreversible altering of crystalline phase of phase-change Ge–Sb thin films

“…12 As-sputter-deposited films are amorphous metastable solid solutions. The threshold is clearly related to the well known explosive crystallization of bulk Sb near room temperature, 14 which at ambient pressure takes on a Peierls' distorted 15 A7 structure, and we have recently shown that Ge-Sb crystallizes in the same structure, 13 with Ge randomly occupying Sb lattice sites. %.…”

Phonon renormalization and Raman spectral evolution through amorphous to crystalline transitions in Sb2Te3 thin films

“…Additionally, similar phase change materials undergo an electronic driven transition. 29 To address the electronic system, transport measurements were done and the measured carrier concentration of a 50 nm film shown in Fig. 4(f) also exhibits a drastic change across the crystallization transition (measurements were taken at 1.9 K after each incremental annealing temperature).…”

Schottky barrier formation at amorphous-crystalline interfaces of GeSb phase change materials

“…In any case, the PCM films studied here have p-type conductivity with Ge acting as a kind of dopant. 7 Furthermore, three types of samples were investigated, where different heating processes were used to achieve partial crystallization of the films (Fig. 1).…”