The mid-infrared (mid-IR) region of the electromagnetic spectrum has a range of applications in defense, sensing, and free space optical communications. However, most mid-IR sources, particularly incoherent emitters, are practically limited as a result of significant non-radiative losses such as Auger and Shockley-Read-Hall recombination as well as phonon-assisted scattering. Recently, plasmonic materials have been a topic of interest due to their ability to overcome traditional limitations of light confinement as well as enhance light-matter interactions. For inherently inefficient sources, such as many mid-IR emitters, coupling of the emitting element to a plasmonic structure could enhance emission efficiency. In this work, we propose and experimentally evaluate the use of plasmon-mediated photoluminescence as a potential method for improving efficiency in mid-IR emitters.
We assess the effectiveness of 3% gallium-doped zinc oxide (G3ZO) as a mid-IR plasmonic material. We design, simulate, fabricate, and characterize a two-dimensional periodic array of bow-tie nanoantennas (nantennas). Our structures are designed to enhance the overlap of the nantenna optical field with underlying In(Ga)Sb/InAs quantum well structures emitting at λ ≈ 4.0μm. Thin films of G3ZO are grown by pulsed laser deposition and are characterized electrically and optically, with the extracted material parameters used as inputs in our simulations. G3ZO plasmonic nantennas are then fabricated by electron-beam lithography and dry-etching. The spectral response of the patterned nantennas is characterized using Fourier transform infrared reflection spectroscopy. Samples are then characterized by temperature and polarization dependent photoluminescence spectroscopy in order to determine the extent to which the emission efficiency improves as a result of coupling to the nanostructures.