High performance dual-band long-wave infrared focal plane array based on type-II InAs/GaSb superlattices

As requirements for infrared (IR) sensing become more stringent, demanding identification of the object rather than mere detection, imagers sensitive to a single waveband are no longer adequate in some applications. In these scenarios, the ability to “see” in multiple wavebands through a single infrared camera is indispensable. For terrestrial-based IR imaging, long-wave (LWIR) detectors are particularly suitable since the emission peaks of room temperature objects are positioned in the 8 to 12μm atmospheric window according to Planck's law. The state-of-the-art dual-band detector systems in the LWIR spectra are based on mercury cadmium telluride, though control of its spatial bandgap uniformity towards this wavelength regime can be challenging [1]. Type-II superlattices (T2SLs) enjoy a unique advantage because of the way its band-structure is determined. The electronic structure of the superlattice is controlled by the layer thicknesses, which is solely determined by the impinging rate of the group III element and does not vary much with the substrate temperature nor the flux ratios. Because of this, a wide range of cutoff wavelengths can be realized with great spatial homogeneity, which is of great benefit for imager operability and manufacturing yield, especially as imager resolutions increase.