Theoretical modeling of growth processes, extended defects, and electronic properties of III‐nitride semiconductor nanostructures

Abstract

Ab initio based simulations have been proven in the past to be and still are a valuable and indispensable tool in the field of III‐nitride semiconductors. They have been successfully used to explain, describe and guide growth and characterization experiments and to address a large variety of material problems at different length scales. In the present report we review on five selected topics which span different length scales, various method developments, and diverse material properties that have been theoretically addressed within the research group “Physics of nitride‐based, nanostructured, light emitting devices.”magnified image Schematic representation of theoretical modeling in synergy with experiment. Left: Ab initio calculated potential energy surface for adatom diffusion on the side facets of a GaN nanowire [theory from L. Lymperakis et al., Phys. Rev. B 79, 241308 (2009), SEM image from T. Aschenbrenner et al., Nanotechnology 20, 075604 (2009)]. Right: Electrostatic potential in a QD calculated by Poisson solver [theory from O. Marquardt et al., J. Appl. Phys. 106, 083707 (2009), HRTEM image from A. Pretorius et al., J. Cryst. Growth 310, 748 (2008)].

Nanoscale x-ray investigation of composition fluctuations in AlGaN nanowires

“…Indeed, for both InGaN and AlGaN alloy layers, spontaneous long range ordering has been experimentally observed, leading to the formation of superlattices along the c-axis [39,40]. First principle calculations have established that such a spontaneous ordering results from the presence of step edges exhibiting (10)(11) facets associated with the existence of two different sites, namely B2 and T1 [41]. In InGaN alloys, Ga is adsorbed on those sites (B2) on the facets where two N bonds can be saturated while In is adsorbed on T1 sites [41,42].…”

“…First principle calculations have established that such a spontaneous ordering results from the presence of step edges exhibiting (10)(11) facets associated with the existence of two different sites, namely B2 and T1 [41]. In InGaN alloys, Ga is adsorbed on those sites (B2) on the facets where two N bonds can be saturated while In is adsorbed on T1 sites [41,42]. By contrast, in AlGaN alloys, Ga is preferentially adsorbed on T1 sites and Al on B2 sites.…”

Density functional theory in materials science

“…For such structures, only the direction normal to the defect shows no periodicity and requires a sufficiently large supercell dimension to avoid image artifacts. In practice, 5–10 atomic layers are often sufficient to separate interactions between the extended defects in neighboring supercells 45. For high‐symmetry static planar defects such as, for example, stacking faults or unreconstructed surfaces supercells as small as O (10) atoms are sufficient to obtain converged results with respect to equilibrium atomic geometry, electronic structure and energy.…”

“…In practice, 5–10 atomic layers are often sufficient to separate interactions between the extended defects in neighboring supercells. 45 For high-symmetry static planar defects such as, for example, stacking faults or unreconstructed surfaces supercells as small as O (10) atoms are sufficient to obtain converged results with respect to equilibrium atomic geometry, electronic structure and energy. These quantities are of high relevance in addressing, for example, the properties of semiconductor heterointerfaces (valence and conduction band offset, impurity segregation), catalytic activity on surfaces, or mechanical strength of polycrystals or precipitate strengthened alloys.…”

The role of surface diffusion in the growth mechanism of III-nitride nanowires and nanotubes

“…The difference in bond length and strength results in preferential incorporation of the metallic species either in the one or the other of the two sites, leading to the formation of a 1:1 spontaneous superlattice. As pointed out by Lymperakis et al[57], the atomic structure of the(10)(11) surface is identical to the structure of the surface created by the formation of a step of height c, which allows one to link SSF to the roughness of the growing surface. The same kind of explanation was invoked by Albrecht et al to account for SSF in AlGaN [58],.…”