Hayton, Jonathan Paul and Krier, Anthony (2017) Development of mid-infrared light emitting diodes to replace incandescent airfield lighting. PhD thesis, Lancaster University.
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Abstract
This work studied the replacement of incandescent airfield lighting systems withlight 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 achievedan output power of 1.2mW at 1.97 um. This device had a wall-plug efficiency of0.7%, an efficiency greater than that obtained in comparable commercially avail-able surface emitting devices. The output power of this device was limited by theconnement of electrons within the quantum dashes at room temperature.Another device characterised in this study was an LED with sub-monolayerInSb/GaSb quantum dots in the active region. The sub-monolayer InSb quantumdots were grown at Lancaster on GaSb substrates using molecular beam epitaxy and fabricated into surface emitting LEDs. These were investigated using x-raydiffraction, 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 uW at a wavelength of 1.66 um.Further devices with InSb sub-monolayer insertions were fabricated into edgeemitting 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 2.5x10^9/cm^2 to 4x10^8/cm^2 between the bottom and top of the defect filtering layer. The edge emitting devices achieved lasing up to 200K 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 uW to 42 uW.In addition, increased confinement also resulted in a decrease in peak wavelength from 2.01um to 1.81um.GaInSb quantum well samples were produced on GaAs substrates utilising aninterfacial misfit array. This included the first reported instances of ternary inter-facial misfit array interfaces with threading dislocation densities of <2x10^9/cm^2 for an AlGaSb/GaAs interface and 5x10^10/cm^2 for an InAlSb/GaAs interface. By utilising an AlGaSb interfacial misfit array it was possible to improve the confinement of carriers within the GaInSb quantum wells, resulting in a twenty fold increase in room temperature photoluminescence intensity.