The lattice-matched XBn structures of InAsSb， grown on GaSb substrates， exhibit high crystal quality， and can achieve extremely low dark currents at high operating temperatures （HOT）. Its superior performance is attributed to the unipolar barrier， which blocks the majority carriers while allowing unhindered hole transport. To further explore the energy band and carrier transport mechanisms of the XBn unipolar barrier structure， this paper systematically investigates the influence of doping on the dark current， photocurrent， and tunneling characteristics of InAsSb photodetectors in the PBn structure. Three high-quality InAsSb samples with unintentionally doped absorption layers （AL） were prepared， with varying p-type doping concentrations in the GaSb contact layer （CL） and the AlAsSb barrier layer （BL）. As the p-type doping concentration in the CL increased， the device’s turn-on bias voltage also increased， and p-type doping in the BL led to tunneling occurring at lower bias voltages. For the sample with UID BL， which exhibited an extremely low dark current of 5×10^-6 A/cm². The photocurrent characteristics were well-fitted using the back-to-back diode model， revealing the presence of two opposing space charge regions on either side of the BL.