AlGaN/GaN core-shell heterostructures for nanowire UV LEDs
Matthew D. Brubaker, Bryan T. Spann, Kristen L. Genter, Alexana Roshko, Paul T. Blanchard, Todd E. Harvey, Kristine A. Bertness
Nanowire-based ultraviolet (UV) LEDs hold great promise as nanoscale light sources, potentially enabling advanced scanning microscopy probes capable of optoelectronic sensing and near-field scanning photolithography. In this work, we report on the synthesis of core-shell nanowire LEDs, including characterization of p-i-n junctions and AlGaN/GaN heterostructures for enhanced injection and confinement of minority carriers. Ordered nanowire arrays were grown on silicon substrates via an N-polar selective area nanowire growth process.1 These silicon-doped nanowire cores were then overcoated with a conformal Mg:GaN shell layer to produce nanowires arrays with p-i-n structure. As shown in Figure 1a, the nanowire LEDs produce electroluminescence under forward bias with emission at 380 nm, corresponding to donor-acceptor-pair recombination in the p-type shell layer. For extending the LED emission towards shorter wavelengths, nanowire arrays with AlGaN shell layers were also grown using conditions identical to those used for the Mg:GaN shells. The AlGaN overcoats were found to exhibit thickness and compositional gradients that depended on the nanowire diameter. As shown in Figure 1b, the thickness of the axial segment of the AlGaN shell was larger in small-diameter nanowires. The Al mole fraction was also observed to decrease for small- diameter nanowires, as determined by photoluminescence measurements (Figure 1c). These observations are consistent with diffusion-induced transport of Ga (but not Al) to the nanowire tip during growth, which effectively increased the axial growth rate and diluted the alloy concentration at the tip. Consequently, AlGaN growth on the nanowire sidewall is expected to be Al-rich (in comparison to the tip) and is tentatively corroborated by the higher energy PL emission peak shown in Figure 1c.
, Spann, B.
, Genter, K.
, Roshko, A.
, Blanchard, P.
, Harvey, T.
and Bertness, K.
AlGaN/GaN core-shell heterostructures for nanowire UV LEDs, Nanowire Week Abstract Book, Hamilton, -1
(Accessed May 19, 2022)