Growth kinetics and substrate stability during high-temperature molecular beam epitaxy of AlN nanowires

Abstract

We study the molecular beam epitaxy of AlN nanowires between 950 and 1215 °C, well above the usual growth temperatures, to identify optimal growth conditions. The nanowires are grown by self-assembly on TiN(111) films sputtered onto Al2O3. Above 1100 °C, the TiN film is seen to undergo grain growth and its surface exhibits {111} facets where AlN nucleation preferentially occurs. Modeling of the nanowire elongation rate measured at different temperatures shows that the Al adatom diffusion length maximizes at 1150 °C, which appears to be the optimum growth temperature. However, analysis of the nanowire luminescence shows a steep increase in the deep-level signal already above 1050 °C, associated with O incorporation from the Al2O3 substrate. Comparison with AlN nanowires grown on Si, MgO and SiC substrates suggests that heavy doping of Si and O by interdiffusion from the TiN/substrate interface increases the nanowire internal quantum efficiency, presumably due to the formation of a SiNx or AlOx passivation shell. The outdiffusion of Si and O would also cause the formation of the inversion domains observed in the nanowires. It follows that for optoelectronic and piezoelectric applications, optimal AlN nanowire ensembles should be prepared at 1150 °C on TiN/SiC substrates and will require an ex situ surface passivation.

ScN/GaN(11̅00): A New Platform for the Epitaxy of Twin-Free Metal–Semiconductor Heterostructures

“…The N and Sc fluxes were calibrated by determining the growth rate of GaN and ScN layers grown in N-limited and Sc-limited regimes, respectively. The temperature was calibrated as described in ref . GaN NWs were grown via self-assembly on sputtered TiN films decorated with Si seeds, as further described in ref .…”

AlN Nanowire-Based Vertically Integrated Piezoelectric Nanogenerators

“…The TiN is highly conductive and can be used as a bottom electrode for nanowire devices. Exact details of their growth and structural analyses were described elsewhere. ,, The N-polar GaN nanowires were grown on a highly doped n-type Si(111) substrate with a thin AlN buffer layer. In this case, a conductive Si substrate was used as the bottom contact of the nanowires.…”

“…This fact likely stems from the limited availability of AlN nanowires, whose synthesis is rather demanding . Recently, it was shown that high crystal quality and vertically aligned AlN nanowires can be achieved using plasma-assisted molecular beam epitaxy (PAMBE). , In this work, we implement such AlN nanowires in vertically integrated nanogenerator (VING) architecture and perform detailed investigations on their direct piezo-response characteristics, as well as evaluate their potential for mechanical sensing and energy-generating applications.…”

Geometrical Selection of GaN Nanowires Grown by Plasma-Assisted MBE on Polycrystalline ZrN Layers

“…The growth of GaN NWs on monocrystalline metallic substrates of proper crystallographic orientation solves the problem [ 24 ], but makes the whole fabrication procedure much more complicated. Interestingly, the high stability of metallic TiN buffers allowed the recent successful PAMBE growth of high-quality AlN NWs at an exceptionally high growth temperatures of ~1200 °C [ 25 , 26 ].…”