Electronic structures of GaN edge dislocations (original) (raw)
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Ab-initio tight-binding study of the core structures of the c -edge dislocation in wurtzite GaN
physica status solidi (a), 2006
In the framework of ab-initio tight-binding methods, we modelled and studied the atomic and electronic core structures of the c-edge basal dislocation in wurtzite GaN. We found this dislocation to have four core configurations displaying 5/8/5-or 4/8-atom rings structures. All these configurations induce unfilled deep states in the top half of band gap.
Strain Induced Deep Electronic States around Threading Dislocations in GaN
Physical Review Letters, 2004
Combining through-focus high-resolution transmission electron microscopy and hierarchical multiscale simulations consisting of density-functional theory, analytical empirical potentials, and continuum elastic theory we demonstrate the existence of a new dislocation type in GaN. In contrast with all previously identified or suggested dislocation structures in GaN, all core atoms are fully coordinated; i.e., no broken bonds occur, implying that the dislocation should be electrically inactive. However, as we show, the giant local strain-field around the dislocation core, in combination with the small lattice constant of GaN, causes deep defect states and thus electrically active edge dislocations independent on the specific core structure.
The atomic configurations of the threading dislocation in GaN
Computational Materials Science, 2002
The atomic structure of the 1=3 h1 1 2 0i edge dislocation has been simulated with the Stillinger-Weber empirical potential which was previously modified to take into account the homopolar bonds, Ga-Ga and N-N. This dislocation is characterised by a multiple structure based on rings of 4, 8 or 5=7 atoms. This multiplicity is explained by considering the position of the origin of the displacements corresponding to the creation of the dislocation. These displacements are imposed according to the isotropic linear elasticity theory. The choice of the origin is equivalent to consider the nature, differently spaced, of the two f1 0 1 0g prismatic planes. The tips of these two planes form the dislocation cores: 5=7atom ring for the less spaced planes and 4 or 8-atom ring for the more spaced planes.
Charge accumulation at a threading edge dislocation in gallium nitride
Applied Physics Letters, 1999
We have performed Monte Carlo calculations t.o determine the charge accumulation on &reading edge dislocations in GaN as a function of the dislocation density and background dopant density. Four possible core structures have been examined, each of which produces defect levels in the gap and may therefore act as electron or hole traps. Our results indicate that charge accumulation, and the resulting electrostatic interactions, can change the relative stabilities of the different. core structures. Structures having Ga and N vacancies at the dislocation core are predicted to be st.able under nitrogen-rich and gallium-rich growth conditions, respectively. Due to dopant depletion at. high dislocat.ion density and the rnult.itude of charge states, the line charge exhibits complex crossover behaxior as the dopant. and dislocat.ion densities vary. Gallium nit,ride films grown on sapphire substrates t y p ically contain bet.ween lo8 and 1O'O threading dislocations per cm2 as a result* of the subst,ant,ial film-substrate chemical and 1att.ice mismatch.l Nevertheless, it. has been possible t.0 fabricate bright and efficient light,-emitt.ing diodes from films composed of GaN alloyed wit.h InN and A1N.2 This success led several researchers t.o specu1at.e early on t.hat t.hreading dislocat.ions in GaN might not act. as efficient. minority-carrier recombination sit.es.' Recent. experiment.al studies, however, have confirmed that there is significant opt.ica13 and elect.rica14 activity associat,ed with these defects. In particular, results from a recent. scanning-capacit.ance microscopy study5 suggest that dislocations are negatively charged in n-type GaN, and studies of transverse mobility in n-type GaN indicate that elect,rons are scattered from these negatively charged dislocations.
Manifestation of edge dislocations in photoluminescence of GaN
Physica B-condensed Matter, 2005
A GaN layer was grown by molecular beam epitaxy on a freestanding GaN template prepared by hydride vaporphase epitaxy. Two characteristic areas have been found in the overgrown layer: a region nearly free from dislocations and a region with the density of the edge dislocations of $5 Â 10 9 cm À2 , as determined by transmission electron microscopy. Low-temperature photoluminescence spectrum from the former contained only well-known exciton lines, whereas the spectrum of the defective area contained additional lines at 3.21 and 3.35 eV. These lines are attributed to unidentified point defects trapped by the edge threading dislocations. r
Origin of the unusually strong luminescence ofa-type screw dislocations in GaN
Physical Review B, 2014
Based on luminescence studies and density functional theory calculations we identify the origin of the unusually strong luminescence of a-type screw dislocations in GaN. In contrast to previous models where only a localization of the holes was considered, density functional theory calculations show a localization of both electrons and holes in the dislocation strain field. This strain field causes a mixing of the s-type state at the conduction band minimum with the next highest state that has p character and is thus susceptible to the shear strain induced by the dislocation.
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
Journal of Electronic Materials, 2020
Electrical and optical properties of grown-in and freshly introduced dislocations in GaN have been studied by the electron beam induced current and cathodoluminescence methods. It is observed that the recombination properties of grown-in and freshly introduced basal plane and threading dislocations are comparable. That allows to assume the intrinsic nature of dislocation recombination activity in GaN. It is demonstrated that the recombination properties of basal plane dislocations weakly depend on their type. The behavior of dislocation-related luminescence at 3.1 eV is more complex. It can be observed not in all GaN crystals even when dislocations are introduced in the similar conditions. Besides, it is not observed on basal plane and threading grown-in dislocations. This luminescence is not produced by freshly introduced basal plane dislocations. These observations can be explained assuming that the dislocation-related luminescence is associated with point defects generated by dislocations gliding in pyramidal or prismatic slip planes.
Materials Science and Engineering: B, 1999
The active layers of GaN contain high densities of threading dislocations, which do not seem to exhibit important electrical activity. It is possible that this may change with time. About 90% are a type, with 1/3 112(0 Burgers vector and their line parallel to the [0001] growth direction, the remaining 10% are a+ c and pure edge c dislocations. High resolution electron microscopy investigation shows that the atomic structure of the a threading dislocations corresponds to 5/7 or eight atom ring cores with rather equal frequency. In modelling the a+ c dislocation, it is shown that only the a component is visible in the images along the [0001], and that the effect of the screw component is spread symmetrically all over the area surrounding the dislocation core.
Electronic structure of 1/6〈2023〉 partial dislocations in wurtzite GaN
Journal of Applied Physics, 2011
The I 1 intrinsic basal stacking faults (BSFs) are acknowledged as the principal defects observed on f11 20g (a-plane) and f1 100g (m-plane) grown GaN. Their importance is established by recent experimental results, which correlate the partial dislocations (PDs) bounding I 1 BSFs to the luminescence characteristics of GaN. PDs are also found to play a critical role in the alleviation of misfit strain in hetero-epitaxially grown nonpolar and semipolar films. In the present study, the energetics and the electronic structure of twelve edge and mixed 1=6h20 23i PD configurations are investigated by first principles calculations. The specific PD cores of the dislocation loop bounding the I 1 BSF are identified for III-rich and N-rich growth conditions. The core structures of PDs induce multiple shallow and deep states, attributed to the low coordinated core atoms, indicating that the cores are electrically active. In contrast to edge type threading dislocations no strain induced states are found.