nBn based infrared detectors using type-II InAs/(In,Ga)Sb superlattices

The development of type-II InAs/(In,Ga)Sb superlattice (SL) detectors with nBn design for single-color and dual-color operation in MWIR and LWIR spectral regions are discussed. First, a 320 x 256 focal plane array (FPA) with cutoff wavelength of 4.2 μm at 77K with average value of dark current density equal to 1 x 10-7 A/cm2 at Vb=0.7V (77 K) is reported. FPA reveals NEDT values of 23.8 mK for 16.3 ms integration time and f/4 optics. At 77K, the peak responsivity and detectivity of FPA are estimated, respectively, to be 1.5 A/W and 6.4 x 1011 Jones, at 4 μm. Next, implementation of the nBn concept on design of SL LWIR detectors is presented. The fabrication of single element nBn based long wave infrared (LWIR ) with λc ~ 8.0 μm at Vb = +0.9 V and T = 100K detectors are reported. The bias dependent polarity can be exploited to obtain two color response (λc1 ~ 3.5 μm and λc2 ~ 8.0 μm) under different polarity of applied bias. The design and fabrication of this two color detector is presented. The dual band response (λc1 ~ 4.5 μm and λc2 ~ 8 μm) is achieved by changing the polarity of applied bias. The spectral response cutoff wavelength shifts from MWIR to LWIR when the applied bias voltage varies within a very small bias range (~100 mV).