Ga-N

Abstract: An ionic-covalent interatomic potential for GaN is developed by combining the Tersoff potential with electrostatic energy, where charges are determined self-consistently with atomic positions using the charge equilibration method of Streitz and Mintmire. The electrostatic parameters of both elements are derived from their experimental ionization energies and electron affinities, whereas the rates of decay of electron densities are represented by Slater's 1s orbitals and optimized to reproduce net atomic charges obtained from DFT data using the DDEC6 charge partitioning scheme. The incorporation of variable charges resolves a long-standing error in degenerate ground state between the wurtzite and zincblende structures and correctly predicts wurtzite as the ground state. As a consequence, the model predicts finite stacking fault energy, which is shown to be in excellent agreement with DFT calculations. The potential demonstrates transferability across wurtzite, zincblende and rocksalt structures, and yields the formation energies of native point defects consistent with DFT results. Under high pressure, the model predicts a phase transition from wurtzite to rocksalt at 48 GPa, consistent with measurements based on X-ray diffraction.

Abstract: Modified embedded-atom method (MEAM) interatomic potentials for the Ga-N and In-N binary and Ga-In-N ternary systems have been developed based on the previously developed potentials for Ga, In and N. The potentials can describe various physical properties (structural, elastic and defect properties) of both zinc-blende and wurtzite-type GaN and InN as well as those of constituent elements, in good agreement with experimental data or high-level calculations. The potential can also describe the structural behavior of Ga_1-xIn_xN ternary nitrides reasonably well. The applicability of the potentials to atomistic investigations of atomic/nanoscale structural evolution in Ga_1-xIn_xN multi-component nitrides during the deposition of constituent element atoms is discussed.

Abstract: Results obtained by atomic computer simulation based on an adapted Stillinger–Weber (SW) potential concerning the structure and relative stability of lattice dislocations, tilt and twin boundaries in GaN are discussed. The method used for the search and description of all possible atomic configurations depends on the crystallographic structure; consequently it is of general application and the results are transferable to the wurtzite binary compounds. On the contrary, the relaxed structures and their relative energetic stability are potential dependent. The results presented here correspond to a GaN model described by a pair potential. Whenever it has been possible our results have been compared with experiments or with ab initio calculations. We present the core shape and energy of a and c crystal dislocations of both edge and screw character; [0001] tilt boundaries of misorientation angles from 9.3° (corresponding to Σ37) to θ = 44.8° (corresponding to Σ43) and (10-1n) twin boundaries (n = 1, 2, 3) [1, 2, 3, 4]. The atomic structures of the tilt boundaries can be described in terms of the three stable structures of the prism a-edge dislocation core. The (10-13) twin boundary is entirely described by 6-coordinated channels whereas the other twin boundaries present more complex structural units.

Abstract: An analytical bond-order potential for GaN is presented that describes a wide range of structural properties of GaN as well as bonding and structure of the pure constituents. For the systematic fit of the potential parameters reference data are taken from total-energy calculations within the density functional theory if not available from experiments. Although long-range interactions are not explicitly included in the potential, the present model provides a good fit to different structural geometries including defects and high-pressure phases of GaN.