InAs/GaSb type-II superlattice light-emitting diodes were fabricated to form a device that provides emission over the entire 3–5 μm mid-infrared transmission window. Variable bandgap emission regions were coupled together using tunnel junctions to emit at peak wavelengths of 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.4 μm, 4.7 μm, and 5.0 μm. Cascading the structure recycles the electrons in each emission region to emit several wavelengths simultaneously. At high current densities, the light-emitting diode spectra broadened into a continuous, broadband spectrum that covered the entire mid-infrared band. When cooled to 77 K, radiances of over 1 W/cm2 sr were achieved, demonstrating apparent temperatures above 1000 K over the 3–5 μm band. InAs/GaSb type-II superlattices are capable of emitting from 3 μm to 30 μm, and the device design can be expanded to include longer emission wavelengths.

Cascaded superlattice LEDs were designed, grown, fabricated, and tested with an n-type anode structure consisting of a variably doped n-GaSb buffer layer and a variable tunnel junction of n-GaxIn1−xAsySb1−y/p-GaSb in place of a conventional p-doped anode contact layer. The elimination of p-doped contact layers from the structure was found to reduce parasitic optical absorption and ohmic loss. After selecting the ideal design from the 4 stage test structures, a nominally identical 16 stage n-type anode structure was grown, yielding an MWIR radiance of 6.7 W/cm2/sr.

InAs/GaSb mid-wave, cascaded superlattice light emitting diodes are found to give higher radiance when epitaxially grown on mismatched GaAs substrates compared to lattice-matched GaSb substrates. Peak radiances of 0.69 W/cm2-sr and 1.06 W/cm2-sr for the 100 × 100 μm2 GaSb and GaAs-based devices, respectively, were measured at 77 K. Measurement of the recombination coefficients shows the shorter Shockley-Read-Hall recombination lifetime as misfit dislocations for growth on GaAs degrade the quantum efficiency only at low current injection. The improved performance on GaAs was found to be due to the higher transparency and improved thermal properties of the GaAs substrate.

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