XBn and XBp infrared detectors

XBn and XBp barrier detectors grown from III-V materials on GaSb substrates have recently been shown
to exhibit a low diffusion limited dark current and a high quantum efficiency (QE). Two important
examples are InAsSb/AlSbAs based XBn devices with a cut-off wavelength of AC ~ 4.1µm, and
InAs/GaSb type II superlattice (T2SL) based XBp devices, with AC ~ 9.5µm. The former exhibit
background limited performance (BLIP) at F/3 up to nearly 200 K, which is a much higher temperature
than observed in standard generation-recombination (G-R) limited devices such as InSb photodiodes,
operating in the same Mid Wave IR (MWIR) atmospheric window. The Long Wave IR (LWIR) T2SL
XBp device has a BLIP temperature of ~100K at F/2. Using the k . p and optical transfer matrix methods,
full spectral response (SR) curves of both detectors can be predicted quite accurately from a basic
knowledge of the layer thicknesses and doping. The SR curves of LWIR gallium free InAs /
InAs1-xSbx XBn and XBp devices have also been simulated. These devices have a lower QE than the
equivalent InAs/GaSb XBp device, due to their lower absorption coefficients. In the XBn case, a small
diffusion length is also expected, which may further reduce the QE.

Keywords: Infrared Detector, Focal Plane Array, Type II superlattice, Gallium free superlattice, Bariode, XBn, XBp,
pBp, LWIR.

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