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In this paper we have investigated dark current sources in high-operating temperature HgCdTe p B nN p + + and InAsSb p B nn p + + and p B nN p + + barrier infrared detectors fabricated using metal organic chemical vapour deposition and molecular beam epitaxy, respectively. The bulk leakage and surface leakage components of the dark current were determined for unpassivated devices fabricated in a round mesa geometry and in different sizes, from 100 to 500 μm diameters. Results show that the surface leakage current depends on both the conductivity types of the active layers and the semiconductor surfaces. In the InAsSb p B nn p + + detector the bulk component constitutes 100% of the total dark current flowing through the heterostructure. Since the absorber region has the same conductivity type in its bulk and at its surface, the unipolar barrier blocks the current in the bulk, and also blocks the current along the n-type surface of the device. For the HgCdTe p B pN p + + detector, the bulk component constitutes about 50% of the total dark current density in the 200 μm device operating at 230 K and −0.1 V, whereas for the InAsSb p B pN p + + detector this share is much higher and amounts to 98%. In the HgCdTe detector, the surface leakage current is attributed to the sidewall surfaces along the absorber, as well as depleted surface. In InAsSb, the surface states are pinned into the conduction band, thus the surface current is limited and comes mainly from the depleted area.

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The paper presents the numerical analysis of the performance of the nBn type-II superlattice barrier detector operated at 230 K. Results of theoretical predictions were compared to the experimental data for the nBn detector composed of AlAs0.15Sb0.85 barrier and InAs (5.096 nm)/InAs0.62Sb0.38 (1.94 nm) superlattice absorber and contact layer. Detector structure was grown on GaAs substrate using molecular beam epitaxy. To determine the position of the electron miniband and the first heavy hole state in the superlattice, we have used a k·p model which can also predict the absorption spectrum and the cut-off wavelength of an absorber layer. As shown, the most important parameters in the nBn structure optimization is the barrier height in the valence band. While the barrier in the conduction band must be high enough to prevent the flow of the electron current from the contact layer to the absorber, the barrier in the valence band must be sufficiently low to ensure the flow and a collection of optically generated holes. The position of the valence band edge for the AlAsSb barrier was changed by changing the valence band bowing parameter for this ternary material. Proper fit of the calculated plot to our experimental data was obtained assuming no bowing in the valence band for AlAsSb barrier.