Reversed resistivity change in GST - Dr. Lin Wang

OCTOBER 29, 2015

Solid-state materialscan be categorized by their ordering levels into crystalline, amorphous, quasi-crystalline, and crystalline but containing amorphous unites phases. Crystalline and amorphous materials are two most common matters in condensedmatter physics and materials science. Under ambient conditions, it is well known that the amorphous phase normally exhibits a higher resistivity, exceeding its crystalline counterpart by 2–5 orders of magnitude. New study indicated that such pronounced resistivity contrast is remarkably reduced and even reversed with increasing hydrostatic-like pressure in the prototypical phase-change material GeSb2Te4 (GST).

Utlizing diamond-anvil-cell technology combined with theoretical simulations, new research co-authored by Dr. Zhenhai Yu and Dr. Lin Wang from HPSTAR studied the high-pressure electrical property of GeSb₂Te₄, a typical phase-change material, observed a pressure-inducedreverse of resistivity contrast.

This anomalous resistivity-reversal originates from the atomic rearrangement during phasetransition under high pressure, which is also confirmed by molecular dynamic simulations. At pressure below 7 GPa, only relatively smallchanges happened in the band structure. In contrast, in amorphous GST, the fraction of voids changes drastically with pressure and the Peierls-like distortion is largely reduced, yet the average bond length remains almost constant. These effects eventually turn the semiconducting glass into ametallic phase.

“This 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-changememory devices”, said Zhenhai Yu.

Caption:Experimental setup for high-pressure resistivity measurement (left); Resitivity(right up) as well as fraction vacancies (right down) varying with pressure in GST.

The study is published recently by Advanced Electronic Materials.

This work is a result of joint efforts from RWTH & HPSTAR. The high pressure experiments were carried out at HPSTAR with our newly developed transport measurement system. The calculations were done by groups from RWTH Aachen University.The other authors are M. Xu, M. Wuttig, Institute of Physics (IA), RWTH Aachen University,Germany. R. Mazzarello, Institute for Theoretical Solid State Physics, JARA-FIT and JARA-HPC,RWTH Aachen University, Germany.