Mid-wavelength infrared photodetectors incorporated into a unipolar barrier architecture with a bulk InAsxSb1-x absorber and an AlSb barrier layer are demonstrated. An extended cutoff was achieved by increasing the lattice constant from 6.09 Å of the GaSb substrate to 6.13 Å using a 1.5 μm thick AlSb buffer layer. This enabled the growth of bulk absorber material with a higher antimony content, InAs0.81Sb0.19, and a greater than 5 μm cutoff. Transitioning the lattice to 6.13 Å also enabled the implementation of a simple binary AlSb layer as a unipolar barrier to block majority carrier electrons and reduce dark current noise. Individual test devices with 4 μm thick absorbers displayed 150 K dark current density, cutoff wavelength, quantum efficiency, and specific detectivity of 3 x 10-5 A/cm2, 5.31 μm, 44 % at 3.4 μm, and 4.3 x 1011 cmHz1/2/W at 5 μm, respectively. The instantaneous dark current activation energy at a given bias and temperature was determined via Arrhenius analysis from the dark current vs. temperature and bias data, and a discussion of valence band alignment between the InAsxSb1-x absorber and AlSb barrier layers is presented. The carrier concentration, mobility, and lifetime of the bulk absorber material and the device performance will be presented and a discussed.