InAs/InAsSb type-II superlattice (T2SL) materials hold great promise for the development of mid-wavelength infrared photodetectors operating at high temperatures, as they avoid the defects caused by Ga atoms in InAs/GaSb T2SL and exhibit long minority carrier lifetime. To reduce the dark current, minority carrier unipolar barrier structures, such as nBn detectors, are commonly employed. In mid-wavelength infrared InAs/InAsSb T2SL nBn photodetectors, the multielement alloy such as AlAsSb is typically utilized as the barrier layer to block the transport of majority carriers. However, the small valence band offset (VBO) between the barrier and absorption layers leads to the saturation of photocurrent at high bias voltage, resulting in increased dark current. In this work, an AlAsSb/InAsSb T2SL barrier was designed to eliminate the VBO and reduce the bias dependency of quantum efficiency. The results show that the fabricated nBn photodetector exhibits a 50% cutoff wavelength of 4.5 μm at 150 K. The optical response of the photodetector saturates under a small bias of -50 mV, achieving a peak responsivity of 1.82 A/W at 3.82 μm and a quantum efficiency of 58.8%. At 150 K and -50 mV applied bias, the photodetector exhibits a dark current density of 2.01×10^-5 A/cm² and a specific detectivity of 6.47×10¹¹ cm·Hz^1/2/W.