Abstract
A tight-binding method is used to obtain the average local order parameter for random and partially ordered ${\mathrm{GaInP}}_{2}$ from the electric field gradients (EFG's) at $\mathrm{Ga}$ sites. The EFG's are obtained from $^{71}\mathrm{Ga}$ nuclear magnetic resonance (NMR). The calculations employed a 17-atom cluster consisting of a central $\mathrm{Ga}$, 4 nearest-neighbor $\mathrm{P}$, and 12 second-nearest-neighbor $\mathrm{Ga}$ or $\mathrm{In}$ atoms. In partially ordered ${\mathrm{GaInP}}_{2}$ there are 8192 such clusters. Distortions from perfect tetrahedral symmetry are obtained using a force balance method with an undistorted bond length of $2.45\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ (average lattice approximation). Comparisons with the NMR data are obtained for a sample grown by liquid phase epitaxy (LPE), which approximates a random sample, and for a sample grown by organometallic vapor phase epitaxy (OMVPE), which is partially ordered. The random assumption provides good agreement with experiment for the LPE sample, and a least-squares fit to the data for the OMVPE sample yields a local order parameter of $0.4\ifmmode\pm\else\textpm\fi{}0.1$.
Published Version
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