Abstract: We developed a numerical capacitance-voltage (C-V) model for InAsSb XBn devices using the Sentaurus TCAD simulation platform to elucidate the capacitance response mechanism of InAsSb barrier infrared detectors. The effects of barrier layer doping type/concentration/thickness, absorber doping, and contact doping on the C-V characteristics are systematically investigated, revealing distinct capacitance-limiting mechanisms: nBn devices are governed by barrier dielectric response, whereas pBn devices are controlled by interface depletion evolution. nBn and pBn single-element photodetectors based on InAs_0.91Sb_0.09 were fabricated and characterized via C-V measurements over a temperature range of 77-290 K, with particular emphasis on extracting the effective carrier concentrations of each functional layer at 150 K. The results show that the effective carrier concentration of the nBn absorber layer increases from 1.0×10¹⁶ cm^-3 at 100 K to 1.35×10¹⁶ cm^-3 at 150 K, with the barrier layer exhibiting a doping concentration of 2.6×10¹⁵ cm^-3 for the pBn device at 150 K, the absorber and barrier layer doping concentrations are determined to be 3.3×10¹⁵ cm^-3 and 3.2×10¹⁶ cm^-3, respectively. This study provides a theoretical foundation for quantitative doping characterization and structural optimization of InAsSb barrier infrared detectors.