Hybrid top-down/bottom-up fabrication of regular arrays of AlN nanorods for deep-UV core–shell LEDs

Core-shell nanostructures are predicted to highly improve the efficiency of deep-UV light emitting diodes (LEDs), owing to their low defect density, reduced quantum-confined Stark effect, high-quality non-polar growth and improved extraction efficiency. In this paper, we report on the nanofabrication of high-quality AlN nanorod arrays using a hybrid top-down/bottom-up approach for use as a scaffold for UV LED structures. We describe the use of Displacement Talbot Lithography to fabricate a metallic hard etch mask to allow AlN nanorod arrays to be dry etched from a planar AlN template. In particular, we investigate the impact of etching parameters on the nanorod etch rate, tapering profile and mask selectivity in order to achieve vertical-sided nanorod arrays with high aspect ratios. AlN facet recovery is subsequently explored by means of regrowth using Metal Organic Vapor Phase Epitaxy. Low pressure and high V/III ratio promote straight and smooth sidewall faceting, which results in an improvement of the optical quality compared to the initial AlN template. The promising results open new perspectives for the fabrication of high-efficiency deep-UV-emitting core-shell LEDs.