Keen, James and Krier, Anthony (2018) Characterisation and simulation of InAs/InAsSb structures for mid-infrared LEDs. PhD thesis, Lancaster University.
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Abstract
This work reports research on InAs/InAsSb structures focusing on their photoluminescence and electroluminescence spectra over the 4 – 300 K temperature range. The purpose was to gain an insight into developing mid – infrared light – emitting diodes (LEDs) operating with sufficiently high power and efficiency for room temperature gas sensing applications. InAs/InAsSb strained – layer superlattice (SLS) and multiple quantum well (MQW) structures of low antimony content (Sb = 3.7 – 13.5 %) grown by MBE on InAs substrates were compared. These structures were characterised by XRD and TEM imaging. Band structure simulations highlighted the effects of changing QW antimony content and layer thicknesses on the emission properties. Mid – infrared 4 – 300 K photoluminescence showed peak shifting to longer wavelengths and intensity reduction for structures with increased QW antimony content. Excitonic emission identified in the photoluminescence spectra under low excitation power was investigated. Temperature quenching was attributed to competing radiative and non – radiative free carrier recombination processes. At higher temperatures, MQW photoluminescence was dominated by emission from electron – hole recombination in the InAs barrier layers. This was not observed for the SLS, with holes strongly confined in the QWs up to room temperature. The dominant Auger process was identified to differ between the MQW and SLS structures, with larger experimental values for these processes compared to theory indicating some degree of suppression due to the type II band alignment of the structures. All these findings highlighted the superiority of the SLS and its attractiveness for use in the active region of MIR LEDs. Two prototype SLS LEDs were fabricated. Mid – infrared 7 – 300 K electroluminescence was obtained, with the 4.2 µm CO2 absorption fingerprint identifiable. The electroluminescence spectra displayed similar behaviour to the PL spectra. Microwatt output powers were produced by the devices at room temperature. Approaches to improve device performance are considered, as it is of interest to further develop SLS LEDs for mid – infrared applications.