Tight-binding calculations of NMR transitions in random and partially ordered GaInP2 -: art. no. 224207

A tight-binding method is used to obtain the average local order parameter for random and partially ordered GaInP2 from the electric field gradients (EFG's) at Ga sites. The EFG's are obtained from Ga-71 nuclear magnetic resonance (NMR). The calculations employed a 17-atom cluster consisting of a central Ga, 4 nearest-neighbor P, and 12 second-nearest-neighbor Ga or In atoms. In partially ordered GaInP2 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 Angstrom (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+/-0.1.