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Significantly improved carrier lifetimes in very long wavelength infrared (VLWIR) InAs/GaInSb superlattice (SL) absorbers are demonstrated by using time-resolved microwave reflectance (TMR) measurements. A nominal 47.0 Å InAs/21.5 Å Ga0.75In0.25Sb SL structure that produces an approximately 25 μm response at 10 K has a minority carrier lifetime of 140 ± 20 ns at 18 K, which is an order-of-magnitude improvement compare to previously reported lifetime values for other VLWIR detector absorbers. This improvement is attributed to the strain-engineered ternary SL design, which offers a variety of epitaxial advantages and ultimately leads to the improvements in the minority carrier lifetime by mitigating defect-mediated Shockley-Read-Hall (SRH) recombination centers. By analyzing the temperature dependence of TMR decay data, the recombination mechanisms and trap states that currently limit the performance of this SL absorber are identified. The results show a general decrease in the long-decay lifetime component, which is dominated by SRH recombination at temperatures below ~30 K, and by Auger recombination at temperatures above ~45 K. This result implies that minimal improvement can be made in the minority carrier lifetime at temperatures greater than 45 K without further suppressing Auger recombination through proper band engineering, which suggests that the improvement to be gained by mitigation of the SRH defects would not be substantial at these temperatures. At temperatures lower than 30 K, some improvement can be attained by mitigated of the SRH recombination centers. Since the strain-balanced ternary SL design offers a reasonably good absorption coefficient and many epitaxial advantages during growth, this VLWIR SL material system should be considered a competitive candidate for VLWIR photodetector technology.
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