  We demonstrate the self-assembled formation of AlN nanowires by molecular
beam epitaxy on sputtered TiN films on sapphire. This choice of substrate
allows growth at an exceptionally high temperature of 1180 {\deg}C. In contrast
to previous reports, the nanowires are well separated and do not suffer from
pronounced coalescence. This achievement is explained by sufficient Al adatom
diffusion on the substrate and the nanowire sidewalls. The high crystalline
quality of the nanowires is evidenced by the observation of near band edge
emission in the cathodoluminescence spectrum. The key factor for the low
nanowire coalescence is the TiN film, which spectroscopic ellipsometry and
Raman spectroscopy indicate to be stoichiometric. Its metallic nature will be
beneficial for optoelectronic devices employing these nanowires as the basis
for (Al,Ga)N/AlN heterostructures emitting in the deep ultraviolet spectral
range.

Materials Science