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32. Structural and electronic properties of <italic>a</italic>-edge dislocations along ⟨1-100⟩ in GaN.

Author

Giaremis, S., Komninou, Ph., Kioseoglou, J., Belabbas, I., and Chen, J.

Subjects
*COMPUTATIONAL chemistry, *STRUCTURAL analysis (Science), *MOLECULAR dynamics, *DENSITY functional theory, *EDGE dislocations, *GALLIUM nitride
Abstract

Computational analysis via molecular dynamics and density functional theory simulations elucidated the structural and electronic properties of a-type basal edge dislocations lying in the ⟨1–100⟩ direction in wurtzite GaN. As a particular and predominant type of misfit dislocations, experimentally identified in coherently grown semipolar heterostructures, understanding of their properties at the atomistic level is crucial for exploring the growth conditions of the material and improving its performance in its various applications. A total of six core configurations are revealed for the first time and investigated systematically. The energetic hierarchy of these core configurations and their electronic structures are determined. The two shuffle core configurations 3-1 and 4-2 are found to be energetically favorable with respect to the glide 2-2 core in both polarities. It is demonstrated that all the core configurations of the a-type basal dislocations introduce multiple gap states which leads to a narrowing of the bandgap in comparison to that of the pristine material, with the N-polar configurations having a more pronounced and detrimental impact. The presence of Ga-related dangling bonds in the vicinity of the core is widely observed, leading to a shift of the Fermi level to the related s orbitals. [ABSTRACT FROM AUTHOR]

Published
2018
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33. Compositional and strain analysis of In(Ga)N/GaN short period superlattices.

Author

Dimitrakopulos, G. P., Vasileiadis, I. G., Bazioti, C., Smalc-Koziorowska, J., Kret, S., Dimakis, E., Florini, N., Kehagias, Th., Suski, T., Karakostas, Th., Moustakas, T. D., and Komninou, Ph.

Subjects
SUPERLATTICES, SCANNING transmission electron microscopy, QUANTUM well devices, QUANTUM electronics, ALLOY analysis
Abstract

Extensive high resolution transmission and scanning transmission electron microscopy observations were performed in In(Ga)N/GaN multi-quantum well short period superlattices comprising two-dimensional quantum wells (QWs) of nominal thicknesses 1, 2, and 4 monolayers (MLs) in order to obtain a correlation between their average composition, geometry, and strain. The high angle annular dark field Z-contrast observations were quantified for such layers, regarding the indium content of the QWs, and were correlated to their strain state using peak finding and geometrical phase analysis. Image simulations taking into thorough account the experimental imaging conditions were employed in order to associate the observed Z-contrast to the indium content. Energetically relaxed supercells calculated with a Tersoff empirical interatomic potential were used as the input for such simulations. We found a deviation from the tetragonal distortion prescribed by continuum elasticity for thin films, i.e., the strain in the relaxed cells was lower than expected for the case of 1 ML QWs. In all samples, the QW thickness and strain were confined in up to 2 ML with possible indium enrichment of the immediately abutting MLs. The average composition of the QWs was quantified in the form of alloy content. [ABSTRACT FROM AUTHOR]

Published
2018
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