Molecular dynamics simulation for evaluating melting point of wurtzite-type GaN crystal

Abstract

Impact response and dynamic strength of partially melted aluminum alloy J. Appl. Phys. 112, 053511 (2012) Study of strain fields caused by crystallization of boron doped amorphous silicon using scanning transmission electron microscopy convergent beam electron diffraction method J. Appl. Phys. 112, 043518 (2012) A theory for time-dependent solvation structure near solid-liquid interface J. Chem. Phys. 136, 244502 (2012) A new model of chemical bonding in ionic meltsA two-phase molecular dynamics simulation of coexisting solid and liquid has been carried out to investigate the melting point of wurtzite-type GaN crystals. The melting point is determined by examining the movement of the interface between the solid and liquid during the simulation. The potential is a two-body interatomic one composed of the long-range Coulomb interaction, the Gilbert-type short-range repulsion, the covalent bonding and covalent repulsion of the modified Morse type, and the van der Waals interaction. The melting point and the interface morphology depend on the crystallization direction. The melting point T m ͑K͒ increases with pressure P ͑GPa͒, but there appears a discontinuity in the vicinity of 8 -9 GPa. This is due to the solid-electrolyte-like behavior of Ga atoms with a partial charge in the high-pressure region. The discontinuity has not yet been confirmed by experiment. The least-squares fitted result is T m = 2538+ 177P − 4.62P 2 at pressures lower than 8 GPa and T m = 2825+ 210P −5P 2 at pressures higher than 9 GPa. The Clausius-Clapeyron relation is confirmed using calculated thermodynamic data.

The Spatial Distribution of Threading Dislocations in Gallium Nitride Films

“…Also, the trends shown in Figure 3 are independent of the TD reduction method used, suggesting that a common process (such as dislocation movement) is involved in each. Regarding possible dislocation movement mechanisms, although dislocation glide has already been observed at room temperature as a result of the high shear stresses experienced under a nanoindenter tip, [38,39] such conditions are not relevant to those encountered in a wafer during the growth process and the evidence presented in this paper points instead towards the occurrence of dislocation climb, which is a very different (thermally activated) process involving the diffusion of vacancies towards dislocation cores. This process can be promoted by isotropic stresses and is expected to occur only at elevated temperatures.…”

“…Our observations are consistent with the classic metallurgical 'recovery' process, in which thermally activated TD motion at temperatures >0.3T m promotes TD annihilation and produces low-energy arrays of TDs with the same Burgers vector, mediating areas of local misorientation. [37] Typical GaN growth temperatures (at $0.5T m [38] ) are well within the recovery regime. Also, the linear arrays are directed along <11-20>, allowing local strain energy reduction due to the overlap of the edge TD strain fields (b edge ¼ 1 / 3 <11-20>).…”

Evaluation of melting point of UO2 by molecular dynamics simulation

“…In general, the melting point obtained from the MD simulation seems to be higher than the experimental one if MD calculations are performed for the homogeneous solid phase at the initial state (one-phase simulation). In order to avoid such misunderstanding, the MD calculation should be performed for the inhomogeneous initial state which consists of solid and liquid phases (so-called the joining two 'boxes' [14] or twophase simulation [15,16]). More recently, Govers et al discussed the melting point of UO 2 in terms of an interatomic potential function [14].…”

Modeling amorphous thin films: Kinetically limited minimization

“…Similarly to the 1-and 5-eV impacts, the 30-eV impact also equilibrates in less than 1 ps, i.e., the same order of magnitude as the phonon frequency. Such fast dissipation times do not allow for full equilibration of the molten state, which typically requires 1-2 orders of magnitude longer timescales [7,24]. (Note that the heat-diffusion laws based on the macroscopic thermal conductivity overestimate the lifetime because the size of the thermal spike is much smaller than the phonon mean free path.)…”