Local ordering in Ge/Ge–Sn semiconductor alloy core/shell nanowires revealed by extended x-ray absorption fine structure (EXAFS)

Author:

Lentz J. Zach1ORCID,Woicik J. C.2ORCID,Bergschneider Matthew3ORCID,Davis Ryan4ORCID,Mehta Apurva5ORCID,Cho Kyeongjae3ORCID,McIntyre Paul C.14ORCID

Affiliation:

1. Department of Materials Science and Engineering, Stanford University 1 , Stanford, California 94305, USA

2. Materials Measurement Science Division, Material Measurement Laboratory, National Institute of Standards and Technology 2 , Gaithersburg, Maryland 20899, USA

3. Department of Materials Science and Engineering, University of Texas at Dallas 3 , Richardson, Texas 75080, USA

4. Stanford Synchrotron Radiation Lightsource (SSRL), SLAC National Accelerator Laboratory 4 , Menlo Park, California 94025, USA

5. Linac Coherent Lightsource (LCLS), SLAC National Accelerator Laboratory 5 , Menlo Park, California 94205, USA

Abstract

Short-range atomic order in semiconductor alloys is a relatively unexplored topic that may promote design of new materials with unexpected properties. Here, local atomic ordering is investigated in Ge–Sn alloys, a group-IV system that is attractive for its enhanced optoelectronic properties achievable via a direct gap for Sn concentrations exceeding ≈10 at. %. The substantial misfit strain imposed on Ge–Sn thin films during growth on bulk Si or Ge substrates can induce defect formation; however, misfit strain can be accommodated by growing Ge–Sn alloy films on Ge nanowires, which effectively act as elastically compliant substrates. In this work, Ge core/Ge1−xSnx (x ≈ 0.1) shell nanowires were characterized with extended x-ray absorption fine structure (EXAFS) to elucidate their local atomic environment. Simultaneous fitting of high-quality EXAFS data collected at both the Ge K-edge and the Sn K-edge reveals a large (≈ 40%) deficiency of Sn in the first coordination shell around a Sn atom relative to a random alloy, thereby providing the first direct experimental evidence of significant short-range order in this semiconductor alloy system. Comparison of path length data from the EXAFS measurements with density functional theory simulations provides alloy atomic structures consistent with this conclusion.

Publisher

AIP Publishing

Subject

Physics and Astronomy (miscellaneous)

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