Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb₂Te₄ Using High Pressure

Abstract

Phase‐change memory devices distinguish “1” and “0” states by the electrical contrast between the amorphous and the crystalline phases. Under ambient conditions, the amorphous phase normally exhibits a higher resistivity, exceeding its crystalline counterpart by 2–5 orders of magnitude. Here, however, it is demonstrated that such pronounced resistivity contrast is remarkably reduced and even reversed with increasing hydrostatic‐like pressure in the prototypical phase‐change material GeSb2Te4 (GST). This anomalous resistivity reversal originates from the differences in the pressure‐induced atomic rearrangement of these two phases, as revealed by ab initio molecular dynamics simulations. Specifically, a low to medium pressure (<7 GPa) primarily compresses the bonds in crystalline GST without significantly displacing the atoms and vacancies off the lattice sites. As a result, only relatively small changes in the band structure are induced. In contrast, in amorphous GST, the fraction of voids changes drastically with pressure and the Peierls‐like distortion is greatly reduced, yet the average bond length remains almost constant. These effects eventually turn the semiconducting glass into a metallic one. Our work reveals distinct behaviors of amorphous and crystalline phase‐change materials under stress, shedding light on the mechanisms of electronic transport in different phases, and thus may have important implications on the design of phase‐change memory devices.

Pressure-Induced Structural Phase Transition and a Special Amorphization Phase of Two-Dimensional Ferromagnetic Semiconductor Cr2Ge2Te6

“…It has been demonstrated that the applied pressure plays an important role in influencing the crystal structure and the associated physical properties such as the resistivity contrast in the phase-change memory material GeSb 2 Te 4 . 44 The pressureinduced structural phase transition in CGT is expected to alter its electronic properties, which can be reflected by the measured resistance plotted in Figure 6(a). The resistance shows a rapid decrease for phase  within the measured pressure range.…”

Structural disorder in the high-temperature cubic phase of GeTe

“…6 is a clear example how local distortions and the disorder of such distortions affect the band gap. On the one hand, the ordered c-GeTe (without PLD) has narrower band gap than the ordered r-GeTe by $0.34 eV, majorly because the PLD in r-GeTe opens the band gap, 16,34 and meanwhile, the so-called resonant bonding in the completely ordered c-GeTe is strengthened, leading to the small band gap. 50 On the other hand, the disordered GeTe has smaller band gap than the ordered one (all with distortion), but the difference is not signicant (0.1-0.2 eV).…”

Evolution of short- and medium-range order in the melt-quenching amorphization of Ge2Sb2Te5

“…As the Peierls-like distortion (PLD) is one of the major structural features in phase change materials, [57][58][59] we also study it in the 6-fold octahedrons with different cutoff values of structure fitting scores, as shown in Figure 5. Here the PLD factor is obtained by averaging the differences of long-and short-bonds in the diagonal lines of each octahedron (e.g.…”

“…Interestingly, both the distortion factors of Ge-and Sb-centered 6-fold octahedral structures concentrate at the vicinity of 0.45 Å, in line with the previous reports. 57,58 This indicates that even though the shape of octahedral clusters may vary (characterized by different structure fitting scores), the intrinsic PLD remains at the same level and thus they may equally contribute to a similar band gap. Therefore, the PLD factor derived from ACA method can effectively reflect the distortion of local structure in amorphous GST and its electronic structure.…”