Self-Assembled formation of long, thin, and uncoalesced GaN nanowires on crystalline TiN films

TL;DR

This paper explores the self-assembled growth of long, thin GaN nanowires on TiN films via molecular beam epitaxy, highlighting their resistance to coalescence and potential for heterostructure applications.

Contribution

It demonstrates that TiN substrates enable the growth of uncoalesced GaN nanowires with controlled density, differing from Si substrates due to adatom diffusion effects.

Findings

GaN nanowires grow long and thin on TiN without coalescence

Diffusion-induced repulsion limits nanowire density on TiN

Nanowire ensembles on TiN are promising for heterostructure growth

Abstract

We investigate in detail the self-assembled nucleation and growth of GaN nanowires by molecular beam epitaxy on crystalline TiN films. We demonstrate that this type of substrate allows the growth of long and thin GaN nanowires that do not suffer from coalescence, which is in contrast to the growth on Si and other substrates. Only beyond a certain nanowire length that depends on the nanowire number density and exceeds here 1.5 {\mu}m, coalescence takes place by bundling, i.e. the same process as on Si. By analyzing the nearest neighbor distance distribution, we identify diffusion-induced repulsion of neighboring nanowires as the main mechanism limiting the nanowire number density during nucleation on TiN. Since on Si the final number density is determined by shadowing of the impinging molecular beams by existing nanowires, it is the difference in adatom surface diffusion that enables on TiN the formation of nanowire ensembles with reduced number density. These nanowire ensembles combine properties that make them a promising basis for the growth of core-shell heterostructures.