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The barrier layer in InAs/GaSb LWIR nBn detector is usually composed of AlGaSb alloy, which has a non-negligible valence band offset and is sensitive to chemical solutions. In this work, we investigated a type-II superlattice (T2SL) barrier that is homogeneous with the T2SL absorber layer in order to resolve these drawbacks of the AlGaSb barrier. The lattice mismatch of the T2SL barrier was smaller than that of the AlGaSb barrier. At − 70 m V and 80 K, the dark current density and the noise equivalent temperature difference of the nBn devices with the T2SL barrier were 4.4 × 1 0 − 6 A / c m 2 and 33 mK, respectively.

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The surface effects on the spontaneous polarisation in ferroelectric thin films were discussed based on the Iaing model in a transverse field. Both the modifications of the transverse field and the strength of coupling in the surface layer were taken into consideration. At the temperature much lower than the Curie point, the behaviour of the spontaneous polarisation deviates from the phenomenological description. The surface effects might lead to the spontaneous polarization and tbe Curie temperature changing in different direction. The theory gives a reasonable description of the experimental temperature dependence of the spontaneous polarisation of triglycine sulfate thin films in the Literature.