A modified empirical potential for energetic calculations of planar defects in GaN (original) (raw)
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Computational Materials Science, 2000
The Stillinger±Weber potential has been parametrized for GaN with bond-type dependent parameters to allow ef-®cient atomic simulations of large systems containing wrong, dangling and extra bonds. The input data for the ®t are the experimental elastic constants of wurtzite structure and wrong bond energies deduced from ab initio calculation. The potential in then applied to zincblende structure and to planar defects. The predicted values are compared to experimental observation and previous computations. Ó
Intrinsic Defect Properties in GaN Calculated By Ab Initio and Empirical Potential Methods
Physical Review B, 2004
Density functional theory (DFT) has been used to investigate the formation, properties, and atomic configurations of vacancies, antisite defects and interstitials in GaN, and the DFT results are compared with those calculated by molecular dynamics simulations using two representative potentials. The DFT calculations reveal that the relaxation of vacancies is generally small, but the relaxation around antisite defects is large, especially for the Ga antisite that is not stable and converts to a N + -N͗0001͘ split interstitial plus a Ga vacancy at the original site. The N interstitials, starting from all possible sites, eventually relax into a N + -N͗1120͘ split interstitial. In the case of Ga interstitials, the most stable configuration is a Ga octahedral interstitial, but the energy difference among all the interstitials is small. The Ga + -Ga͗1120͘ split interstitial can bridge the gap between nonbonded Ga atoms, thereby leading to a chain of four Ga atoms along the ͗1120͘ direction in GaN. The formation energies of vacancies and antisite defects obtained using the Stillinger-Weber (SW) potential are in reasonable agreement with those obtained by DFT calculations, whereas the Tersoff-Brenner (TB) potential better describes the behavior of N interstitials. In the case of Ga interstitials, the most stable configuration predicted by the TB model is a Ga + -N͗1120͘ split interstitial; while for the SW model the Ga tetrahedral configuration is more stable, which is in contrast to DFT results.
Microstructure of planar defects and their interactions in wurtzite GaN films
Solid-state Electronics, 2003
A formulation of the Stillinger–Weber empirical potential is presented and employed for energetic calculations of various planar defects in GaN. The energies of inversion domain boundaries and of the I1 stacking fault on the basal plane were calculated and compared to those of ab initio calculations from the literature. Present modification of empirical potential yielded comparable results with ab initio calculations. The potential was then applied for relaxation of large supercells comprising junction lines between inversion domain boundaries and stacking faults. The relaxed structures were used for HRTEM image simulations, which were compared with the corresponding experimental observations.
Philosophical Magazine, 2006
Results obtained by atomic computer simulation based on an adapted Stillinger-Weber (S-W) 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. 24/06/10 2 Contents 1 INTRODUCTION 2 COMPUTATIONAL METHOD 2.1 CONSTRUCTION OF SIMULATION CELLS 2.2 EMPIRICAL POTENTIAL DESCRIBING ATOMIC INTERACTIONS IN GAN 2.3 RELAXATION PROCEDURE 3 RESULTS 3.1 ATOMIC STRUCTURE AND ENERGY OF DISLOCATIONS 3.2 ATOMIC STRUCTURE AND ENERGY OF TILT BOUNDARIES 3.3 DISLOCATIONS MOBILITY AND BOUNDARY-DISLOCATION INTERACTION 3.4 ATOMIC STRUCTURE AND ENERGY OF TWIN BOUNDARIES
Physica Status Solidi (c), 2003
In epitaxial wurtzite GaN, structural transformations of inversion domain boundaries on prismatic planes are observed at their junctions with basal stacking faults. The admissible line defects formed at these junctions are constructed and relaxed using a modified Stillinger-Weber potential. Fourteen stable admissible interactions are identified. The calculated energies of the interactions are discussed in relevance to the associated dislocations. High resolution electron microscopy observations are compared with simulated images obtained from the relaxed atomic configurations.
Theoretical Study of Gallium Nitride Molecules, GaN 2 and GaN 4
Journal of Physical Chemistry A, 2008
The electronic and geometric structures of gallium dinitride GaN 2 , and gallium tetranitride molecules, GaN 4 , were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4 ( 2 B 1 ) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2 , while 37 structures were identified for GaN 4 corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4 . The dissociation energy of the ground-state GaN 2 (X 2 Π) is 1.1 kcal/mol with respect to Ga( 2 P) + N 2 (X 1 Σ g + ). The ground-state and the first two excited minima of GaN 4 are of 2 B 1 (C 2V ), 2 A 1 (C 2V , five member ring), and 4 Σ g -(D ∞h ) symmetry, respectively. The dissociation energy (D e ) of the ground-state of GaN 4 , X 2 B 1 , with respect to Ga( 2 P) + 2 N 2 (X 1 Σ g + ), is 2.4 kcal/mol, whereas the D e of 4 Σ gwith respect to Ga( 4 P) + 2 N 2 (X 1 Σ g + ) is 17.6 kcal/mol.
Theoretical Study of Gallium Nitride Molecules, GaN2 and GaN4
Journal of Physical Chemistry A, 2008
The electronic and geometric structures of gallium dinitride GaN 2 , and gallium tetranitride molecules, GaN 4 , were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4 (2 B 1) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2 , while 37 structures were identified for GaN 4 corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4. The dissociation energy of the ground-state GaN 2 (X 2 Π) is 1.1 kcal/mol with respect to Ga(2 P) + N 2 (X 1 Σ g +). The ground-state and the first two excited minima of GaN 4 are of 2 B 1 (C 2V), 2 A 1 (C 2V , five member ring), and 4 Σ g-(D ∞h) symmetry, respectively. The dissociation energy (D e) of the ground-state of GaN 4 , X 2 B 1 , with respect to Ga(2 P) + 2 N 2 (X 1 Σ g +), is 2.4 kcal/mol, whereas the D e of 4 Σ gwith respect to Ga(4 P) + 2 N 2 (X 1 Σ g +) is 17.6 kcal/mol.
Theoretical Investigation on the Electronic and Geometric Structure of GaN 2 + and GaN 4
Journal of Physical Chemistry A, 2007
The electronic and geometric structures of gallium dinitride cation, GaN 2 + and gallium tetranitride cation, GaN 4 + were systematically studied by employing density functional theory (DFT-B3LYP) and perturbation theory (MP2, MP4) in conjunction with large basis sets, (aug-)cc-pVxZ, x ) T, Q. A total of 7 structures for GaN 2 + and 24 for GaN 4 + were identified, corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces, and bonding mechanisms for some low-lying electronic states. The calculated dissociation energy (D e ) of the ground state of GaN 2 + , X 1 Σ + , is 5.6 kcal/mol with respect to Ga + ( 1 S) + N 2 (X 1 Σ g + ) and that of the excited state, ã 3 Π, is 24.8 kcal/mol with respect to Ga + ( 3 P) + N 2 (X 1 Σ g + ). The ground state and the first excited minimum of GaN 4 + are of 1 A 1 (C 2V ) and 3 B 1 (C 2V ) symmetry with corresponding D e of 11.0 and 43.7 kcal/mol with respect to Ga + ( 1 S) + 2N 2 (X 1 Σ g + ) for
Energetics of the 30 ∘ Shockley partial dislocation in wurtzite GaN
Superlattices and Microstructures, 2006
In the present work, we have investigated the relative energy of different core configurations of the 30∘ Shockley partial dislocation in wurtzite GaN. By using a modified Stillinger–Weber potential, we have carried out large scale calculations on models containing many thousands of atoms. Both glide and shuffle configurations have been considered within the two core polarities (Ga, N). Similarly to what was reported for conventional semiconductors, our calculations showed that the reconstructed glide configurations are energetically favoured over the shuffle ones.
Atomic structures and energies of partial dislocations in wurtzite GaN
Physical Review B, 2004
The atomic structures of 1 / 6͗2023͘ partial dislocations delineating the I 1 intrinsic basal stacking fault in wurtzite GaN are modelled using an empirical interatomic potential in combination with anisotropic elasticity calculations. Twelve stable configurations are obtained for each polarity, and their core radii, energies, and atomic configurations are given. The 5 / 7-atom ring core in which the atoms are tetrahedrally coordinated is found energetically favorable among the edge dislocation configurations. For the mixed type partials, 5 / 7-and 12-atom rings are obtained as low-energy cores, but none of them is found to comprise only tetrahedrally coordinated atoms. Each of them is found energetically favorable under distinct structural conditions.