Density functional theoretical study of surface structure and adatom kinetics for wurtzite AlN

Abstract

Density-functional calculations concerning the structure and stability of wurtzite AlN surfaces are presented. Specifically, (0001) and (0001¯) polar surfaces and (11¯00) and (112¯0) nonpolar surfaces are discussed in detail. Binding energies, migration pathways, and diffusion barriers for relevant adatoms such as Al, Ga, and N on these polar and nonpolar surfaces are determined. The calculation indicates low diffusion barrier for Al adatom on Al terminated (0001) surface, whereas the N adatom seems to have lower diffusion barrier on N terminated (0001¯) surfaces. A strong anisotropy was observed for diffusion behavior for Al adatom on (11¯00) and (112¯0) surfaces in the [112¯0] and [0001] directions, respectively.

Self‐Assembly of Well‐Separated AlN Nanowires Directly on Sputtered Metallic TiN Films

“…The NW axis corresponds to the ⟨0001⟩ axis of the wurtzite crystal, and we identified the crystallographic orientation of the sidewall facets following the method reported by Largeau et al, by combining top‐view SEM images with X‐ray pole figures. Remarkably, {110} sidewalls are found, although according to density‐functional theory calculations, the surface energy of these planes is larger than for {100} facets . The latter ones form on self‐assembled GaN NWs, but {110} sidewalls were reported also for (Al,Ga)N NWs grown by MBE .…”

Kinetic instability of AlGaN alloys during MBE growth under metal-rich conditions on m-plane GaN miscut towards the -c axis

“…The growth phase diagram of nonpolar m-plane AlGaN/ GaN heterostructures is not completely established, [13][14][15][16][17][18][19] unlike the corresponding process for similar c-plane structures. Evident differences arise from the anisotropy of adatom mobilities along the c-and a-axis on the m-plane surface during growth, 20,21 and the anisotropic lattice mismatch between GaN and AlN along the c-direction (4%) and the a-direction (2.5%). Equally importantly, however, the m-plane surface and its primary step edges (c-type and a-type) present atomic composition and dangling bond geometries that are markedly different from those available for growth on the c-plane surface.…”

High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

“…However, epitaxy of AlN template with low TDD remains a challenge due to the serious mismatch between AlN and sapphire in terms of lattice constant and thermal expansion coefficient. Moreover, due to the low surface mobility of Al adatoms caused by high diffusion barriers and very strong Al-N bonding3, it is hard to tailor the growth process for AlN as that for GaN adopting the “two-step” approach, which thus results in a very high TDD in AlN films, typically in the order of 10 9 –10 10 cm −2 . High TDD reduces the internal quantum efficiency (IQE) of DUV multiple quantum wells (MQWs) significantly because of nonradiative recombination of carriers at dislocations.…”