Deep UV Emission from Highly Ordered AlGaN/AlN Core-Shell Nanorods.

Three-dimensional core-shell nanostructures could resolve key problems existing in conventional planar deep UV light-emitting diode (LED) technology due to their high structural quality, high-quality nonpolar growth leading to a reduced quantum-confined Stark effect and their ability to improve light extraction. Currently, a major hurdle to their implementation in UV LEDs is the difficulty of growing such nanostructures from Al _x Ga _{1- x} N materials with a bottom-up approach. In this paper, we report the successful fabrication of an AlN/Al _x Ga _{1- x} N/AlN core-shell structure using an original hybrid top-down/bottom-up approach, thus representing a breakthrough in applying core-shell architecture to deep UV emission. Various AlN/Al _x Ga _{1- x} N/AlN core-shell structures were grown on optimized AlN nanorod arrays. These were created using displacement Talbot lithography (DTL), a two-step dry-wet etching process, and optimized AlN metal organic vapor phase epitaxy regrowth conditions to achieve the facet recovery of straight and smooth AlN nonpolar facets, a necessary requirement for subsequent growth. Cathodoluminescence hyperspectral imaging of the emission characteristics revealed that 229 nm deep UV emission was achieved from the highly uniform array of core-shell AlN/Al _x Ga _{1- x} N/AlN structures, which represents the shortest wavelength achieved so far with a core-shell architecture. This hybrid top-down/bottom-up approach represents a major advance for the fabrication of deep UV LEDs based on core-shell nanostructures.