Development of mid-infrared light emitting diodes to replace incandescent airfield lighting.
11 November 2017
This work studied the replacement of incandescent airfield lighting systems with light emitting diodes. The focus was on the replacement of the infrared component of the incandescent spectra. A series of LEDs with a variety of nanostructures in different material systems were produced and tested to determine their suitability in replacing incandescent airfield lighting systems. Utilising quantum dashes in the active region, a surface emitting LED achieved an output power of 1.2 mW at 1.97 µm. This device had a wall-plug efficiency of 0.7%, an efficiency greater than that obtained in comparable commercially available surface emitting devices.
The output power of this device was limited by the confinement of electrons within the quantum dashes at room temperature. Another device characterised in this study was an LED with sub-monolayer InSb/GaSb quantum dots in the active region. The sub-monolayer InSb quantum dots were grown at Lancaster on GaSb substrates using molecular beam epitaxy and fabricated into surface emitting LEDs. These were investigated using x-ray diffraction, transmission electron microscopy and electroluminescence. This is the first reported electroluminescence from such devices. Emission was measured at temperatures up to 250 K. Room temperature emission was from the quantum wells in which the quantum dots where grown, output power was 80 µW at a wavelength of 1.66 µm.
Further devices with InSb sub-monolayer insertions were fabricated into edge emitting diodes. These samples were grown on GaAs using interfacial misfit arrays, defect densities were reduced through the use of defect filtering layers. The threading dislocation density decreased by a factor of 6 from 2.5×109/cm2 to 4×108/cm2 between the bottom and top of the defect filtering layer. The edge emitting devices achieved lasing up to 200 K with a characteristic temperature of 150 K.
These devices were limited by Shockley–Read–Hall recombination and weak confinement of carriers within the InSb regions. The inclusion of AlGaSb barriers improved room temperature operation with output power increasing from 2 µW to 42 µW. In addition, increased confinement also resulted in a decrease in peak wavelength from 2.01 µm to 1.81 µm. GaInSb quantum well samples were produced on GaAs substrates utilising an interfacial misfit array.
This included the first reported instances of ternary interfacial misfit array interfaces with threading dislocation densities of <2×109/cm2 for an AlGaSb/GaAs interface and 5×1010/cm2 for an InAlSb/GaAs interface. By utilising an AlGaSb interfacial misfit array it was possible to improve the con- finement of carriers within the GaInSb quantum wells, resulting in a twenty fold increase in room temperature photoluminescence intensity
Hayton, J.P., 2017. Development of mid-infrared light emitting diodes to replace incandescent airfield lighting (Doctoral dissertation, Lancaster University).
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