A gallium-free alternative finds the middle ground for high operating temperature infrared arrays

The choice of an infrared detector’s component materials has vital implications for its operating characteristics and applications. Since the first use of InSb for IR detection in the 1950s, the lattice structures of many new compounds have offered competitive advantages to such detection applications. The gallium-free InAs/InAsSb type-II strained-layer superlattice (SLS) has emerged as a possible alternative to the more common InAs/GaSb superlattice type, with simpler growth qualities and greater defect tolerance. Comparison of both types at the NASA Jet Propulsion Laboratory, as described in Applied Physics Letters, demonstrate that the desired IR operating range is a major factor in determining the best choice for a particular application.

The investigators compared characteristics of InAs/InAsSb and InAs/GaSb type-II superlattices and studied the operation of an InAs/InAsSb superlattice-based mid-wavelength high-operating temperature barrier IR detector (HOT-BIRD). Both types of superlattices displayed differing advantages.

For long-wavelength IR detectors, the gallium-free SLS material is easier to grow and shows better minority carrier lifetime, while the InAs/GaSb version has better optical and hole transport properties. The researchers suggest that neither type has overwhelming advantages over the other and the choice between them should depend upon the desired cutoff wavelength as well as growth and processing qualities. In the mid-infrared, however, the superlattice without gallium appears to show definitively greater suitability.

The HOT-BIRD, whose focal plane array facilitates nature integration into camera systems, can operate at significantly higher temperatures than the InSb types with simpler and less expensive cryogenic requirements. For those applications with lower background scenes that do require detector cooling, HOT-BIRD still shows higher dark current than the most successful IR photodetector material, HgCdTe, but its temperature characteristics can be optimized for intermediate background applications. This demonstration of gallium-free superlattices that can serve as versatile alternatives to HgCdTe and InAs/GaSb superlattices could bring a range of new detectors to the device market.

Source: “Mid-wavelength high operating temperature barrier infrared detector and focal plane array,” by David Z. Ting, Alexander Soibel, Arezou Khoshakhlagh, Sir B. Rafol, Sam A. Keo, Linda Höglund, Anita M. Fisher, Edward M. Luong, and Sarah D. Gunapala, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5033338 .