Infrared detectors play an essential role in the fields of infrared imaging, medical analysis, missile warning, biochemical gas detection and security monitoring. Among them, InAs/InAsSb, a type II superlattice material grown on GaSb substrates, has become a key material for high-performance infrared focal plane arrays due to its outstanding properties. However, InAs/InAsSb T2 SL infrared detectors suffer from high dark current values that limit their performance. To solve this issue, researchers redesigned the barrier structure of the device and investigated the dark current generation mechanism. The nBn-type barrier structure features a large energy barrier in the conduction band, providing self-passivation and effectively reducing the tunneling current. However, in InAs/InAsSb devices with nBn-type barrier structures, it is still challenging to precisely regulate parameters such as doping levels and thicknesses between different structural layers. Therefore, the device structure is investigated through numerical calculations, focusing on the dominant dark current mechanisms and structural characteristics. The optimal parameter configurations are explored to improve the device performance.Based on the structural characteristics of InAs/InAsSb infrared detectors, the dominant mechanisms of dark current and the associated band structure were systematically analyzed. Numerical simulations incorporating Poisson's equation, continuity equations, and heat equations were employed to precisely optimize key parameters, including the doping concentration of the absorption layer (AL), the doping concentration and thickness of the barrier layer (BL), operating temperature, and material composition. The optimized design establishes a high-energy barrier to effectively block majority carriers and allow minority carrier to migrate. By achieving a near-zero valence band offset, the design significantly reduces the dark current in the device.Simulation results indicate that when the Sb composition in the AlAs_1-xSb_x barrier reaches 0.91, the valence band offset approaches zero, facilitating smooth transport of minority carriers across the barrier and significantly reducing the dark current (Fig.3). An increase in the barrier thickness results in a gradual rise in the valence band offset (VBO), which becomes more pronounced when the barrier thickness exceeds 100 nm (Fig.4). For the absorption layer, higher doping levels increase electron concentration and decrease hole concentration, but the impact of doping concentration variations on dark current reduction is minimal (Fig.5). In the barrier layer, higher doping concentrations lead to a higher absolute value of the dark current turn-on voltage. Moreover, excessive doping in the barrier layer results in pronounced band offsets, hindering minority carrier transport (Fig.6). The dark current decreases with lower temperatures, aligning with its expected temperature dependence (Fig.7).Numerical calculations were performed to determine the optimal structural parameters for the nBn barrier-type T2 SL InAs/InAsSb/B-AlAsSb mid-wavelength infrared detector. When the absorption layer doping concentration is precisely controlled at 1×10¹³ cm^-3, the barrier layer doping concentration at 1×10¹⁵ cm^-3, and the barrier layer thickness set to 80 nm, the detector achieves a low dark current density of 4.5×10^-7 A/cm² under a high-temperature condition of 140 K and a bias voltage of -0.5 V. This performance meets the requirements for applications in infrared imaging, medical diagnostics, missile early warning, and related fields.