Performance of mid-wave T2SL detectors with heterojunction barriers

A heterojunction T2SL barrier detector which effectively blocks majority carrier leakage over the pn-junction was designed and fabricated for the mid-wave infrared (MWIR) atmospheric transmission window. The layers in the barrier region comprised AlSb, GaSb and InAs, and the thicknesses were selected by using k · P-based energy band modeling to achieve maximum valence band offset, while maintaining close to zero conduction band discontinuity in a way similar to the work of Abdollahi Pour et al. [1] The barrier-structure has a 50% cutoff at 4.75 μm and 40% quantum efficiency and shows a dark current density of 6 × 10−6 A/cm2 at −0.05 V bias and 120 K. This is one order of magnitude lower than for comparable T2SL-structures without the barrier. Further improvement of the (non-surface related) bulk dark current can be expected with optimized doping of the absorber and barrier, and by fine tuning of the barrier layer design. We discuss the effect of barrier doping on dark current based on simulations. A T2SL focal plane array with 320 × 256 pixels, 30 μm pitch and 90% fill factor was processed in house using a conventional homojunction p–i–n photodiode architecture and the ISC9705 readout circuit. High-quality imaging up to 110 K was demonstrated with the substrate fully removed.