The suppression of dark current and enhancement of epitaxial quality remain critical challenges for mid-wave infrared (MWIR) detectors based on Type-II superlattices (T2SLs). InAs/InAsSb T2SLs offer tunable bandgaps and long carrier lifetimes, yet high defect density in barrier layers and suboptimal barrier design have limited device performance. Therefore, this study focuses on the design of an nBn MWIR detector architecture employing AlAsSb as the unipolar barrier and on optimizing its epitaxial growth parameters to achieve low dark current, high detectivity, and material uniformity.A continuum k·p band-structure model was employed to simulate the coupling between thickness and Sb composition in InAs/InAs_1-xSb_x T2SLs, enabling precise tuning of the 3-5 µm cutoff wavelength (Fig.1). Strain-balanced InAs/InAs_0.6Sb_0.4 superlattices were grown on GaSb (001) substrates via molecular-beam epitaxy (MBE), with substrate rotation and a V/III beam-flux ratio optimized to promote uniform composition and period thickness. High-resolution X-ray diffraction (HRXRD) rocking-curve measurements at four wafer positions quantified period deviation (2.46%) and strain distribution. The AlAs_1-xSb_x barrier layer (x≈0.91) was deposited at three temperatures (385 °C, 400 °C, 420 °C) to assess morphology and strain via atomic-force microscopy (AFM) and reciprocal-space mapping (RSM).HRXRD characterization confirmed exceptionally uniform superlattice growth, with full-width at half-maximum (FWHM) of satellite peaks ranging 19.3''-19.8'' (Fig.3). AFM analysis revealed minimum surface roughness (RMS = 0.252 nm) and reduced defect formation for AlAsSb barriers grown at 400 °C (Fig.6). RSM data demonstrated minimal residual strain under optimized Sb/In and As/In flux ratios (8∶1.8), consistent with RSM measurements (Fig.7). At 77 K and –0.6 V bias, Al₂O₃-passivated devices exhibited dark-current density of 5.30×10^-6 A/cm² and resistance-area product (RA) of 4.13×10⁴ Ω·cm² (Fig.8). Peak specific detectivity reached 8.35×10¹¹ cm·Hz^1/2/W at λ_peak = 4.49 µm, and at the 50% cutoff of 5.00 µm, D* remained 5.01×10¹¹ cm·Hz^1/2/W (Fig.9). This indicates the device’s performance is comparable to MWIR T2SL detectors with similar cut-off wavelengths.The combination of k·p band modeling, strain-balanced MBE growth, and AlAsSb barrier optimization has yielded an nBn InAs/InAsSb T2SL detector with comparable performance in the MWIR range. AFM and RSM results validate the growth‐temperature window (400 °C) that minimizes AlAsSb barrier surface roughness and strain. Al₂O₃ passivation further suppresses surface leakage dark current, enabling D* exceeding 10¹¹ cm·Hz^1/2/W under cryogenic operation. These results validate the feasibility of our barrier-structure design and epitaxial process optimizations, laying a technical foundation for high-performance MWIR Type-II superlattice detectors in large-format focal-plane array applications.