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

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.

Enhanced Radiative Efficiency in GaN Nanowires Grown on Sputtered TiNx: Effects of Surface Electric Fields

“…Last but not least, the exceptionally long exciton lifetime obtained here for the thinnest NWs documents the high crystalline quality achievable for GaN on sputtered TiN. This highly stable, refractory substrate thus provides a robust platform for the fabrication of hybrid metal/semiconductor structures up to very high temperatures …”

“…The same spectral position, corresponding to x = 0.93, 27 is observed for samples B and C after growth. In the XRD profile of sample A (as well as for B and C), we detect a strong and sharp TiN 111 reflection as for stoichiometric TiN, 32 but also two weak additional reflections. The angular position, intensity, and width of these reflections indicate that our TiN x films contain nanoscopic inclusions of Ti and ε-Ti 2 N with a total volume on the order of 1%.…”

“…This highly stable, refractory substrate thus provides a robust platform for the fabrication of hybrid metal/semiconductor structures up to very high temperatures. 32 ■ METHODS TiN x Synthesis. The δ-TiN x films are deposited onto α-Al 2 O 3 (0001) wafers by reactive sputtering of a Ti target in a mixed Ar/N 2 gas environment.…”

Toward Quantitative Measurements of Piezoelectricity in III-N Semiconductor Nanowires

“…The nanowire samples were grown by using plasma-assisted molecular beam epitaxy (PAMBE). Undoped GaN nanowires and undoped Al 0.9 Ga 0.1 N/GaN nanowires were deposited on highly n-doped Si(111) substrates, , while undoped AlN nanowires were grown on a sapphire substrate covered by a conductive TiN layer obtained by sputtering . These nanowires are single crystal and nearly defect-free.…”

“…The polarity of the GaN nanowires is of N-polar, proven by KOH chemical etching, and deduced from high-resolution scanning transmission electron microscopy (HR-STEM) of the equivalent nanowires . The AlN nanowires were suggested to have Al-polarity by HR-STEM analysis of one dispersed AlN nanowire from the same sample . Details of the investigated nanowires are summarized in Table .…”