Abstract
Herein, the self‐assembled formation of AlN nanowires (NWs) by molecular beam epitaxy on sputtered TiN films on sapphire is demonstrated. This choice of substrate allows growth at an exceptionally high temperature of 1180 °C. In contrast to previous reports, the NWs are well separated and do not suffer from pronounced coalescence. This achievement is explained by sufficient Al adatom diffusion on the substrate and the NW sidewalls. The high crystalline quality of the NWs is evidenced by the observation of near‐band‐edge emission in the cathodoluminescence spectrum. The key factor for the low NW coalescence is the TiN film, which spectroscopic ellipsometry and Raman spectroscopy indicate to be stoichiometric. Its metallic nature will be beneficial for optoelectronic devices using these NWs as the basis for (Al,Ga)N/AlN heterostructures emitting in the deep ultraviolet spectral range.
Highlights
Exclusively for the growth by molecular beam epitaxy (MBE).[7,8] The self-assembled formation of AlN NWs is very challenging, and efforts by MBE can be categorized into
We explore the growth of AlN NWs on TiN in this study
Ge(220) hybrid monochromator, and a Ge(220) analyzer. Both the AlN NWs and the TiN film were studied at room temperature by Raman spectroscopy utilizing a laser wavelength of 473 nm
Summary
Ge(220) hybrid monochromator, and a Ge(220) analyzer Both the AlN NWs and the TiN film were studied at room temperature by Raman spectroscopy utilizing a laser wavelength of 473 nm. The former value corresponds to an average vertical growth rate of 3.4 nm minÀ1 (considering the incubation time), that is, much higher than the 2.1 nm minÀ1 expected for planar AlN growth under these fluxes This discrepancy implies that, in addition to the direct impingement of atoms on the NW top facet, there is a significant contribution of adatom diffusion on the sidewalls toward the tip. The extremely high growth temperature promotes adatom diffusion, enhancing vertical growth and reducing parasitic lateral growth
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