Two new superlattices with high internal quantum efficiency at high injection, InAs/AlGaInSb and InAs/GaInSb/InAs/AlAsSb, are presented and compared with state-of-the-art InAs/GaSb and InAs/InAsSb superlattices. The internal quantum efficiency peaks at 44% and 77% for the InAs/AlGaInSb and InAs/GaInSb/InAs/AlAsSb samples, respectively, which suggests that they are excellent candidates for high-efficiency mid-wave infrared LEDs. These values have been measured without invoking the ABC model to eliminate the assumption of Boltzmann statistics. The calculated superlattice band structures are used qualitatively to explain the internal quantum efficiency results.
Efficient mid-infrared light output has been obtained by incorporating a W-superlattice into a cascaded mid-infrared LED structure and by thinning and roughening of the emission side of the structure. At cryogenic temperatures, a radiance of ∼13.4 W/cm2-sr is achieved. Compared to the best published InAs/GaSb mid-IR LED, the maximum radiance is improved by ∼2.0×, while the wallplug efficiency improvement at the maximum radiance is improved >10×. For room temperature measurements on an un-thinned 400 μm diameter diode, the radiance (light output power) for a quasi-continuous wave and 1% duty cycle were ∼ 0.48 W/cm2-sr (2.4 mW) and ∼1.35 W/cm2-sr (6.8 mW), respectively. When compared to previous room temperature 4.2 μm LEDs, at a 1% duty cycle, this LED has optical powers that are 3× brighter. When compared to thermal emitters used in gas sensors, in the quasi-continuous wave, this LED uses ∼100× less energy per measurement.
Low extraction efficiencies continue to be a source of parasitic heating and decreased performance in infrared light-emitting diodes. Research into metasurfaces and the advance of methods used to fabricate these planar structures have made it possible to realize a metalens tailored to increasing the radial output of geometrically constrained superlattice lightemitting diodes (SLEDs). The metalens presented here, which allows for unprecedented control over optical wavefronts on a subwavelength scale, was designed to promote the extraction for an emitter of a specific mid-wave infrared (MWIR) wavelength, dielectric material, and unpolarized, Lambertian output. Results from a representative optical sample showed an enhanced output of 3.3× of the metalens design when compared to a planar surface. We also include results of a design of experiment where metalens performance was tracked as a function of distance from the emitter and the height of nanopillars making up the metalens.
The internal quantum efficiency of a series of InAs/GaSb superlattices was investigated as a function of carrier generation rate through variable excitation, quasicontinuous-wave photoluminescence measurements. GaSb thicknesses were varied to maximize the internal quantum efficiency for midwave infrared emission. Internal quantum efficiencies were determined from measurements of the photoluminescence radiance and extraction efficiencies computed within a two-slab model. The peak internal quantum efficiencies varied from 15% to 29% at 77 K, which is in good agreement with expectations from InAs/GaSb superlattice light-emitting diode performance.
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