From Event: SPIE Optical Engineering + Applications, 2018
In recent years there has been a rapidly increasing demand for energy-efficient and cost effective gas sensors. Of particular interest are CO2 sensors that can find numerous applications in health monitoring, control of air quality and horticulture. A major hurdle comes from the fact that the main CO2 absorption band lies above 4um, where very few cheap and compact sources are commercially available. Amongst the various approaches explored, the indium antimonide material system stands out as a very effective solution for the development of compact Light Emitting Diodes (LEDs). In particular, the quaternary compound AlGaInSb shows great promise as it offers a bandgap type-I alignment, which enables the design of effective multi-quantum well (MQW) active regions.
In this paper we show the great potential of LED structures with strained GaInSb MQWs and AlGaInSb barriers for the next generation of mid-IR emitters at 4.3 um. Different quantum well and barrier compositions were examined through k.p simulations to extract momentum matrix elements and energy levels. The simulations were also used to assess the impact of strain and quantum well width on the efficiency of the radiative transition and to optimise the profile of the carrier injection. Based on the theoretical analysis, a number of different epilayer structures were grown by molecular beam epitaxy and the performance of LEDs with varying geometries were compared. Results confirm that strained MQW structures suppress unwanted transitions by at least one order of magnitude and provide a substantial enhancement in the internal quantum efficiency of the LEDs.
Manuel Reza, Matthew Steer, Calum MacGregor, Iain Thayne, and Marc Sorel, "Strain-compensated GaInSb/AlGaInSb type-I MQW for CO2 detection (Conference Presentation)," Proc. SPIE 10766, Infrared Sensors, Devices, and Applications VIII, 1076608 (Presented at SPIE Optical Engineering + Applications: August 22, 2018; Published: 18 September 2018); https://doi.org/10.1117/12.2320699.5836577123001.
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