Atomic structure and phase stability of InxGa1-xN random alloys calculatedusing a valence-force-field method

We have calculated the atomic structure and strain energy of the InxGa1-xN random alloy (0 less than or equal to x less than or equal to 1) based on 5 92 similar to 13 240-atom models. A valence-force-field method with the Kea ting potential is used for the strain energy calculation. We analyzed the b ond-length and bond-angle distribution in the alloy due to the random fluct uation of the atom positions. The change in the average Ga-N and In-N bond lengths is calculated as a function of the composition x. The calculated re sult is in good agreement with the recent experimental data of the extended x-ray-absorption fine-structure method. The calculated enthalpy of mixing Delta H-m, i.e., the strain energy, versus the composition x is expressed i n the regular-solution model; Delta H-m = Omega x(1-x) using the x-dependen t interaction parameter Omega = -2.11x + 7.41 (kcal/mole). This Omega value is the most reliable among those so far calculated. The calculated phase d iagram shows a broad and asymmetric miscibility gap, e.g., 0.04 less than o r equal to x less than or equal to 0.88 at 800 degrees C. The critical temp erature for phase separation is 1417 degrees C.