Semiconductor superlattices (SLs) have intrigued researchers for more than 40 years due to their electronic properties that reveal the quantum effects occurring in the periodic structure of nanometer-thin layers of differing materials. Mid-infrared SLs have advanced from a material of purely scientific interest to one being practically implemented in devices for detectors and lasers intended for military target recognition, chemical detection, and night vision systems because of the advantages over devices composed of bulk materials. SLs promise larger effective masses, leading to lower tunneling currents, less Auger recombination arising from proper bandgap engineering, longer wavelengths (smaller bandgaps) available than in the individual materials provided from type-II band alignments, and varying bandgaps designed by choosing compositions and layer thicknesses. The advantages of type-II SLs (T2SLs) are expected to lead to lower dark currents, higher operating temperatures, and greater quantum efficiencies for infrared detectors.
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