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See detailInterfaces between nonpolar and semipolar III-nitride semiconductor orientations: Structure and defects
Kioseoglou, Joseph; Lotsari, Antiopi; Kalesaki, Efterpi UL et al

in Journal of Applied Physics (2012), 111

Observations of easy transition between nonpolar and semipolar orientations during III-Nitride heteroepitaxy identify the 90o <-12-10> rotation relationship as being very important in defining this ... [more ▼]

Observations of easy transition between nonpolar and semipolar orientations during III-Nitride heteroepitaxy identify the 90o <-12-10> rotation relationship as being very important in defining this coexistence. A rigorous analysis of this relationship using the topological theory of interfaces showed that it leads to a high order of coincident symmetry and makes energetically favorable the appearance of the intergranular boundaries. Principal low-energy boundaries, that could also be technologically exploited, have been identified by high-resolution transmission electron microscopy (HRTEM) observations and have been studied energetically using empirical potential calculations. It is also shown that these boundaries can change their average orientation by incorporating disconnections. The pertinent strain relaxation mechanisms can cause such boundaries to act as sources of threading dislocations and stacking faults. The energetically favorable (10-10) // (0001) boundary was frequently observed to delimit m-plane crystallites in (-12-12) semipolar growth. [less ▲]

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See detailMorphology and strain of self-assembled semipolar GaN quantum dots in (11-22) AlN
Dimitrakopulos, George; Kalesaki, Efterpi UL; Kioseoglou, Joseph et al

in Journal of Applied Physics (2010), 108

GaN quantum dots (QDs) grown in semipolar (11-22) AlN by plasma-assisted molecular-beam epitaxy were studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy ... [more ▼]

GaN quantum dots (QDs) grown in semipolar (11-22) AlN by plasma-assisted molecular-beam epitaxy were studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy techniques. The embedded (11-22)-grown QDs exhibited pyramidal or truncated-pyramidal morphology consistent with the symmetry of the nucleating plane, and were delimited by nonpolar and semipolar nanofacets. It was also found that, in addition to the (11-22) surface, QDs nucleated at depressions comprising {10-11} facets. This was justified by ab initio density functional theory calculations showing that such GaN/AlN facets are of lower energy compared to (11-22). Based on quantitative high-resolution TEM strain measurements, the three-dimensional QD strain state was analyzed using finite-element simulations. The internal electrostatic field was then estimated, showing small potential drop along the growth direction, and limited localization at most QD interfaces. [less ▲]

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