Development of mid-infrared materials and light emitting diodes

Bond, Philip and Carrington, Peter and Marshall, Andrew and Zhuang, Qiandong and Stowell, Alison (2025) Development of mid-infrared materials and light emitting diodes. PhD thesis, Lancaster University.

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Abstract

Light Emitting Diodes (LEDs) operating in the technologically important mid-infrared (MIR) spectral range (2 – 5 μm) are important for a variety of applications including environmental gas sensing, non-invasive medical diagnosis, and tunable IR spectroscopy. However, MIR LED efficiency at room temperature is still low due to the prevalence of non-radiative recombination. The research presented here is aimed at developing material systems which increase the efficiency of these LEDs, as well creating bright, wavelength specific devices. Furthermore, a novel application for the MIR spectral range was investigated, in detecting plastics based on their spectral fingerprint around 3 μm. This is an important application as black plastics are currently unrecyclable due to their inability to be detected by current optical sorting technologies in plastic recovery facilities (PRFs). Using an analysis of the life cycle of plastics, and black plastics, a discussion is had regarding the necessity of them to remain in the economy and how recycling technologies can be used to increase economic circularity – leading to a more sustainable use of resources. To target the 3 μm region, the InGaAsSb/AlGaAsSb type-I quantum well material system was studied. Samples were grown by MBE on n-GaSb substrates, characterised by x-ray diffraction (XRD) and photoluminescence (PL) spectroscopy to find structural and bandgap characteristics. The samples grown showed emission from 2.1 – 3.4 μm using various quantum well structures. When integrated into an LED, room temperature emission was obtained at ~ 2.8 μm. Due to their Auger quenching mechanisms and reduction in SRH recombination, InAs/InAs1-xSbx superlattices strain balanced to GaSb were studied. These structures were also grown via MBE and characterised using XRD and PL, showing emission ~ 4 μm at 4 K. These superlattices were integrated into LEDs, which showed bright emission ~ 3.9 μm at low temperature, with emission increasing up to 4.5 μm at room temperature.