Light emitting diodes (LEDs) are light sources of great technological importance because of their wide spectral tunability, long lifetimes, and potentially high energy efficiency. It is widely observed, however, that LEDs based on all relevant material platforms exhibit degraded internal quantum efficiency as the emission wavelength is shifted into the green part of the visible spectrum. Increasing device efficiency in this spectral region has therefore become the focus of intense research. In this work we study the use of plasmonic metallic nanostructures as a method for enhancing LED efficiency.

Electromagnetic fields are known to exhibit resonances near metallic nanostructures originating from collective oscillations of the electron gas on the metal surface. Surface plasmon polaritons (SPPs) confined to the surface of a planar metal film, and localized surface plasmons (LSPs) confined to the surface of a nanostructure, feature unique optical properties such as large near optical fields and large modal densities. These spatial and spectral properties are highly dependent on the material and geometric properties of the nanostructure, allowing for extensive engineering of the plasmonic system to meet application needs. Plasmonic nanostructures are currently being studied for use in a wide range of applications such as waveguiding, bio-sensing, surface-enhanced spectroscopy, solid state light emission, and solar cells.

Coupling into both SPP and LSP modes can enhance the spontaneous emission rate of a nearby radiating dipole, by virtue of their large associated local optical fields and high density of modes. Effective scattering of the excited plasmonic resonances into the radiation continuum can then lead to large enhancements in radiated field intensity. In this work, we have studied the application of various metallic nanostructures to nitride semiconductor light emitters to enhance their emission efficiency. Numerical investigations have been conducted to optimize nanostructure geometries, and experimental studies have demonstrated large enhancements in photoluminescence intensity and increased emitter recombination rates. These results indicate that LED emission efficiency can be strongly improved with properly engineered metallic nanostructures, which provides a promising new approach to further increase the performance of commercial devices.