PbSe is a well-known IV-VI photoconductive material, typically operating in the 3-5μm regime at temperatures easily achieved with compact thermoelectric coolers. Recently, Northrop Grumman Corporation has demonstrated PbSe photoconductive pixels down to 12x12 μm2, with quantum efficiencies as high as 15% at 230K. Today’s challenges, however, demand more sensitivity at near room-temperature operation. To this end, the employment of nanoplasmonic antenna for the increased performance of PbSe-based photoconductors has been investigated. Metallic nanostructures have seen a great deal of interest in recent years, due to increased absorption and large field enhancements at the surface plasmon resonance (SPR). These structures are usually reserved for lower wavelength regimes where the incident radiation matches the plasma frequency of the metal. However, by manipulating the size, morphology and surrounding medium of the structure, the surface plasmon resonance can be shifted to longer wavelengths. Indeed, by tuning the electric permittivity of the host material, size, aspect ratio, or combination thereof, the nanoantenna SPR can be tailored to the infrared band of interest. For PbSe photoconductors tuning these nanostructure parameters can result in a large increase in absorption and sensitivity. Herein, we present an examination of several types of nanoantenna including nanospheres, nanorods, and nanodiscs made from Au, Ag, and Pt in various layers of PbSe photoconductive films. Structures have been modeled using Mie theory to determine SPR, as well as finite element modeling to determine the increase in near-field intensity using the full solution of Maxwell’s equations. The presented results demonstrate large increases in absorption, as well as the near-field enhancement of nanoplasmonic antenna employed in PbSe photoconductive films.
In this work, we report on In<sub>x</sub>Ga<sub>1-x</sub>As<sub>1-y</sub>Sb<sub>y</sub>/GaSb structures, where the indium mole fraction (x) varies from x=0 to x<0.50. Although there has been considerable effort to exploit high-indium content In<sub>x</sub>Ga<sub>1-x</sub>As<sub>1-y</sub>Sb<sub>y</sub> for longer wavelength applications, high misfit dislocation densities are inevitable and the miscibility gap remains a formidable barrier. In addition to atomically smooth structures, we observed three-dimensional networks of quantum dashes and other results reveal a self-organized composition modulation. Some physical features of the quantum dashes include near one-micron lengths, 90° flip in orientation, and uniformity across a 20 x 20 μm area. We also observe network formation up to a film thickness of 10-nm.
In this work, we perform spectroscopic studies of AlGaAs/InGaAs quantum cascade laser structures that demonstrate
frequency mixing using strain-compensated active regions. Using a three-quantum well design based on diagonal
transitions, we incorporate strain in the active region using single and double well configurations on various surface
planes (100) and (111). We observe the influence of piezoelectric properties in molecular beam epitaxy grown
structures, where the addition of indium in the GaAs matrix increases the band bending in between injector regions and
demonstrates a strong dependence on process conditions that include sample preparation, deposition rates, mole fraction,
and enhanced surface diffusion lengths. We produced mid-infrared structures under identical deposition conditions that
differentiate the role of indium(strain) in intracavity frequency mixing and show evidence that this design can potentially
be implemented using other material systems.