In situ Measurement of CuPt Alloy Ordering using Strain Anisotropy

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Abstract

The optical and electrical properties of many III-V alloys change with the degree of CuPt atomic ordering, which is very sensitive to growth conditions. The bulk ordered alloy is elongated along the normal to the ordered planes, and is asymmetrically strained when coherent to a cubic substrate. Here, we demonstrate in situ measurement of the anisotropic strain due to ordering using two-dimensional wafer curvature. The measurement is sensitive to bulk anisotropies, and so is complementary to other in situ measurements that are sensitive to surface anisotropies. Using ab initio calculations, we determine a maximum strain anisotropy of 0.27% between [110] and [1̄10] when perfectly ordered single-variant GaInP2 is coherent to a (001) cubic substrate. We relate the in situ measurement of strain anisotropy on various GaInP 2 samples to ex situ measurements of the order parameter to validate the measurement and confirm the capability to predict material properties. The measurement monitors change in ordering during growth, useful for quickly determining the growth condition dependence of ordering or monitoring order-disorder transitions. More generally, this measurement technique could, in principle, be used to monitor phase changes in any epitaxial system for which the strain anisotropy of the two phases differs.

Original languageAmerican English
Article number053502
Number of pages5
JournalJournal of Applied Physics
Volume115
Issue number5
DOIs
StatePublished - 7 Feb 2014

NREL Publication Number

  • NREL/JA-5200-60911

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