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

doi:10.1073/pnas.0812942106

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

^aDepartment of Applied Mathematics, University of Western Ontario, London, ON, Canada N6A5B7;
^bIBM T. J. Watson Research Center, Yorktown Heights, NY 10598;
^cIBM Almaden Research Center, San Jose, CA 95120;
^dPhysics Department, University of California at San Diego, La Jolla, CA 92093; and
^eDepartment of Chemistry, University of Western Ontario, London, ON, Canada N6A5B7

Edited by Mildred S. Dresselhaus, Massachusetts Institute of Technology, Cambridge, MA, and approved May 12, 2009 (received for review December 19, 2008)

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.

Footnotes

To whom correspondence should be addressed. E-mail: krusin{at}us.ibm.com
Author contributions: L.K.-E., D.M.N., G.J.M., and M.H.M. designed research; D.S., R.A.N., L.K.-E., G.J.M., D.M.N., B.G.E., X.-h.L., Z.E.H., S.P., C.C., D.B.S., D.N.B., Y.S., and M.H.M. performed research; S.R. and Y.S. contributed new reagents/analytic tools; L.K.-E., D.M.N., G.J.M., and M.H.M. analyzed data; and L.K.-E., D.M.N., G.J.M., and M.H.M. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
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