High operating temperature epi-InSb and XBn-InAsSb photodetectors

Abstract

In MWIR photodiodes made from InSb, InAs or their alloy InAs1-xSbx, the dark current is generally limited by Generation-Recombination (G-R) processes. In order to reach a background limited operating temperature higher than ~80 K, steps must be taken to suppress this G-R current. At SCD we have adopted two main strategies. The first is to reduce the concentration of G-R centres, by changing from an implanted InSb diode junction to a higher quality one grown by Molecular Beam Epitaxy (MBE). Our epi-InSb diodes have a background limited performance (BLIP) temperature of ~105 K at F/4, in 15 to 30 μm pitch Focal Plane Arrays (FPAs). This operation temperature increase delivers a typical saving in cooling power of ~20%. In order to achieve even higher operating temperatures, we have developed a new XB_nn bariode technology, in which the bulk G-R current is totally suppressed. This technology includes nB_nn and pB_nn devices, as well as more complex structures. In all cases, the basic unit is an n-type AlSb_1-yAs_y / InAs_1-xSb_x barrier layer / photon-absorbing layer structure. These FPAs, with 15 to 30 μm pitch and a cut-off wavelength of ~ 4.1 μm, exhibit a BLIP temperature of ~ 175K at F/3. The cooling power requirement is reduced by ~60% compared with conventional 77K operation. The operation of both our diode and bariode detectors at high temperatures results in an improved range of solutions for various applications, especially where Size, Weight, and Power (SWaP) are critical. Advantages include faster cool-down time and mission readiness, longer mission times, and higher cooler reliability, as well as very low dark current and an enhanced Signal to Noise Ratio (SNR) at lower operating temperatures. This paper discusses the system level performance for cut-off wavelengths appropriate to the sensing materials in each detector type. Details of the radiometric parameters of each detector type are then presented in turn.