Development of InAsSb-based light emitting diodes for chemical sensing systems

Mid-infrared (3--6 {micro}m) LED`s are being developed for use in chemical sensor systems. As rich, InAsSb heterostructures are particularly suited for optical emitters in the mid-infrared region. The authors are investigating both InAsSb-InAs multiple quantum well (MQW) and InAsSb-InAsP strained layer superlattice (SLS) structures for use as the active region for light emitting diodes (LED`s). The addition of phosphorus to the InAs barriers increases the light and heavy hole splitting and hence reduces non-radiative Auger recombination and provides for better electron and hole confinement in the InAsSb quantum well. Low temperature (< 20 K) photoluminescence (PL) emission from MQW structures is observed between 3.2 to 6.0 {micro}m for InAsSb wells between 70 to 100 {angstrom} and antimony mole fractions between 0.04 to 0.18. Room temperature PL has been observed to 6.4 {micro}m in MQW structures. The additional confinement by InAsP barriers results in low temperature PL being observed over a narrower range (3.2 to 5.0 {micro}m) for the similar well thicknesses with antimony mole fractions between 0.10 to 0.24. Room temperature photoluminescence was observed to 5.8 {micro}m in SLS structures. The addition of a p-AlAsSb layer between the n-type active region (MQW or SLS) and a p-GaAsSb contact layer improves electron confinement of the active region and increases output power by a factor of 4. Simple LED emitters have been fabricated which exhibit an average power at room temperature of > 100 {micro}W at 4.0 {micro}m for SLS active regions. These LED`s have been used to detect CO{sub 2} concentrations down to 24 ppm in a first generation, non-cryogenic sensor system. They will report on the development of novel LED device designs that are expected to lead to further improvements in output power