Strain Induced Deep Electronic States around Threading Dislocations in GaN (original) (raw)
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Long range strain and electrical potential induced by single edge dislocations in GaN
Physica B: Condensed Matter, 2006
A dipole like strain state is induced by threading edge dislocations emerging at the surface of gallium nitride (GaN) bulk substrates. This local strain is calculated by means of a three-dimensional elastic deformation potential model, taking into account the free surface of the sample. The calculations are in excellent quantitative agreement with the strain state derived from line shifts of the near band edge excitonic spectrum, measured by micro-photoluminescence ðmPLÞ. Scanning surface potential microscope (SSPM) measurements show that the dipole structure is not reflected in the local electrical potential distortions around the dislocations and the potential profile decreases laterally faster than the strain distortion, which is detectable even in several micrometer distance from the dislocation core.
Electronic structures of GaN edge dislocations
Physical Review B, 2000
We investigate atomic and electronic structures of the threading edge dislocations of GaN using selfconsistent-charge density-functional tight-binding approaches. Full-core, open-core, Ga-vacancy, and N-vacancy edge dislocations are fully relaxed in our total-energy scheme. The Ga-vacancy dislocation is the most stable in a wide range of Ga chemical potentials, whereas full-core and open-core dislocations are more stable than others in the Ga-rich region. Partial dehybridization takes place during the lattice relaxation near the dislocation in all cases. The dangling bonds at Ga atoms mostly contribute to the deep-gap states, whereas those at N atoms contribute to the valence-band tails. All the edge dislocations can act as deep trap centers, except the Ga-vacancy dislocation, which may act as an origin of yellow luminescence.
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.
Mixed partial dislocation core structure in GaN by high resolution electron microscopy
Physica Status Solidi (a), 2006
The core structures of a 1/6 [203] mixed partial dislocation in wurtzite GaN have been investigated using a combination of high resolution transmission electron microscopy, circuit mapping, and image simulation of relaxed models. HRTEM simulated images of relaxed atomic models, derived by energetic calculations with a modified Stillinger–Weber-type empirical interatomic potential, were calculated and compared to the experimental images. Among twenty-four stable core configurations the 12- and 10-atom rings satisfied the experimental contrast. A pattern registration procedure was used for the matching of simulated and experimental HRTEM images. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Dislocation core structures in Si-doped GaN
Applied Physics Letters, 2015
Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10 8 and (10 ± 1) × 10 9 cm-2. All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a+c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a+c)-type cores in Si-doped GaN.
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.
Dislocation reduction in GaN grown on Si(111) using a strain-driven 3D GaN interlayer
Physica Status Solidi B-basic Solid State Physics, 2010
In this paper we demonstrate a strain-driven GaN interlayer method to reduce dislocation densities in GaN grown on (111) oriented silicon by metal organic vapour phase epitaxy (MOVPE). In order to achieve crack-free GaN layers of reasonable thicknesses and dislocation densities it is crucial to integrate both dislocation reduction and strain management layers. In contrast to techniques like FACELO or nanoELO we show the in situ formation of GaN islands directly on the AlN nucleation layer without the need to deposit a SiO2 or SiNx mask. A graded AlGaN layer for strain management can be grown on top of this dislocation reducing 3D GaN inter-layer in order to achieve crack-free GaN layers grown on top of the AlGaN strain management layer. Furthermore, an additional SiNx layer for subsequent dislocation reduction can also be incorporated into the structure and is shown to efficiently reduce the dislocation density down to the low 109 cm−2. The structural properties of the 3D GaN island buffer layer and overgrown samples are studied by means of SEM, cross-sectional, and plan view TEM. Cathodoluminiscence in an SEM is employed to correlate the dislocation microstructure as observed by plan view TEM with luminescent properties.
Imaging dislocations in gallium nitride across broad areas using atomic force microscopy
Review of Scientific Instruments, 2010
We have employed an atomic force microscope with a high sampling rate to image GaN samples grown using an epitaxial layer overgrowth technique and treated with silane and ammonia to enlarge the surface pits associated with threading dislocations (TDs). This allows TDs to be identified in high pixel density images tens of microns in size providing detailed information about the spatial distribution of the TDs. An automated software tool has been developed, which identifies the coordinates of the TDs in the image. Additionally, we have imaged the same sample using Kelvin probe force microscopy, again at high pixel density, providing data about the local changes in surface potential associated with hundreds of dislocations.
Atomic structure and energy of threading screw dislocations in wurtzite GaN
physica status solidi (c), 2005
Atomic structure and energy of the screw dislocation b=<000c> in the full core configuration has been investigated with a self-consistent density functional tight binding calculation. A 288-atom cluster was used and the dangling bonds saturated with pseudo-hydrogen. The line energy is comparable to the values obtained using a supercell.