Well-separated AlN nanowires grown on metallic films

AlN is the material of choice for optoelectronic devices working in the deep ultraviolet (UV) spectral range. However, the use of AlN in applications has been hampered by the lack of native substrates, resulting in high defect densities of AlN thin films. An attractive opportunity is offered by growth in the form of nanowires, which is principally possible on a wider variety of substrates than suitable for thin film growth. Here, we report important advancements for the growth of AlN nanowires.

Bird’s eye (left) and top-view (right) scanning electron micrographs of AlN nanowires grown directly on sputtered metallic TiN films on sapphire.

Previous attempts to grow AlN nanowires resulted in severely coalesced nanowire ensembles. Coalescence leads to crystal defects, foiling the conceptual advantage of nanowires over planar films. As a novel approach, we pioneer AlN nanowire growth by molecular beam epitaxy on sputtered metallic TiN films as substrates. TiN exhibits high chemical and thermal stability, which enables us to use an exceptionally high substrate temperature close to 1200 °C. The high substrate temperature promotes Al adatom diffusion, which in turn facilitates the formation of well-separated nanowires. Their high crystalline quality is evidenced by the observation of near-band-edge luminescence. Beyond the properties of the nanowires themselves, the metallic nature of the TiN film is highly beneficial for optoelectronic devices. The excellent electrical and thermal conductivity of this material improves charge injection and waste heat dissipation. Therefore, the growth of AlN nanowires on TiN introduced in our study opens up new possibilities for the fabrication of high quality AlN/(Al,Ga)N heterostructures emitting in the  deep UV range.

1 Author M. Azadmand , T. Auzelle , J. Lähnemann , G. Gao , L. Nicolai , M. Ramsteiner , A. Trampert , S. Sanguinetti , O. Brandt , L. Geelhaar

Self-assembly of well-separated AlN nanowires directly on sputtered metallic TiN films

Source Phys. Status Solidi-Rapid Res. Lett. , 14 , 1900615 ( 2020 )
DOI : 10.1002/pssr.201900615 | Download arXiv: 1910.07391 | 3149 Cite : Bibtex RIS
M. Azadmand, T. Auzelle, J. Lähnemann, G. Gao, L. Nicolai, M. Ramsteiner, A. Trampert, S. Sanguinetti, O. Brandt, and L. Geelhaar