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There are continuing efforts to develop type-II superlattice (SL) materials for very long wavelength infrared (VLWIR) detector applications. However, the SLs have high residual electron background doping densities that depend on SL growth conditions, which lead to shorter minority carrier lifetime and lower performance parameters than theoretically predicted. In this study, the authors compare the technical advantages of using InAs/GaInSb over InAs/GaSb SL with respect to reducing the electron doping levels. Our temperature-dependent electrical transport measurements show that the InAs/GaInSb SL design has a lower electron density than the InAs/GaSb SL with the same bandgap and have electron densities (mobilities) on the order of the mid 1011 cm−2 (25 000 cm2/V s). Since small period InAs/GaInSb SLs also produce greater Auger recombination suppression for a given VLWIR gap than the large period InAs/GaSb SL, the InAs/GaInSb SL appears to be a better candidate for long lifetime IR materials for future very long wavelength infrared devices. [ABSTRACT FROM AUTHOR]

The impact of post growth annealing on the electrical properties of a long wavelength infrared type-II superlattice (SL) was explored. Quarters of a single SL wafer were annealed at 440 °C, 480 °C, and 515 °C, respectively for 30 min. Changes in the electrical properties were followed using spectral photoconductivity, temperature dependent Hall effect, and time-resolved pump-probe measurements. The bandgap energy remained at ∼107 meV for each anneal, and the photoresponse spectra showed a 25% improvement. The carrier lifetime increased from 12 to ∼15 ns with annealing. The electron mobility was nearly constant for the 440 °C and 480 °C anneals, and increased from ∼4500 to 6300 cm2/Vs for the 515 °C anneal. [ABSTRACT FROM AUTHOR]

We explore the optimum growth space for a 47.0Å InAs/21.5 Å Ga0.75In0.25Sb superlattices (SLs) designed for the maximum Auger suppression for a very long wavelength infrared gap. Our growth process produces a consistent gap of 50 ± 5 meV. However, SL quality is sensitive to the growth temperature (Tg). For the SLs grown at 390-470 °C, a photoresponse signal gradually increases as Tg increases from 400 to 440 °C. Outside this temperature window, the SL quality deteriorates very rapidly. All SLs were n-type with mobility of ∼10 000 V/cm² and 300 K recombination lifetime of ∼70 ns for an optimized SL. [ABSTRACT FROM AUTHOR]

Authors discuss how anion incorporation was controlled during the epitaxial growth process to develop InAs/GaInSb superlattice (SL) materials for very long wavelength infrared applications. A SL structure of 47.0 Å InAs/21.5 Å Ga 0.75 In 0.25 Sb was selected to create a very narrow band gap. Although a molecular beam epitaxy growth developed can produce a strain balanced ternary SL structure with a precisely controlled band gap around 50 meV, the material quality of grown SL layers is particularly sensitive to growth defects formed during an anion incorporation process. Since Group III antisites are the dominant structural defects responsible for the low radiative efficiencies, the authors focus on stabilizing III/V incorporation during SL layer growth by manipulating the growth surface condition for a specific anion cracking condition. The optimized ternary SL materials produced an overall strong photoresponse signal with a relatively sharp band edges and a high mobility of ~10,000 cm 2 /V s that is important for developing infrared materials. [ABSTRACT FROM AUTHOR]