<p>Mercury cadmium telluride (HgCdTe) infrared detectors are strategically important for military, aerospace, and environmental monitoring. Finite-element method (FEM) multiphysics simulations quantify how heterojunction and barrier-layer architectures regulate dark current and quantum efficiency (QE) in mid-wave infrared (MWIR) detectors. Conventional PN devices exhibit the minimum dark current at Cd composition <i>x</i> = 0.4. The P⁺–ν–N⁺ (PvN) heterojunction suppresses dark current by about four orders of magnitude through nonequilibrium carrier suppression. Adding a barrier layer (P⁺–B–ν–N⁺, PBvN) further lowers dark current and improves high-temperature operation via electric field redistribution. Parameter optimization yields an optimal PvN design with a 4 μm absorber doped at 1 × 10¹⁵&#xa0;cm⁻³ and an optimal PBvN design with a 150 nm barrier doped at 5 × 10¹⁵ cm⁻³. The optimized PvN reaches 92% MWIR QE while suppressing short-wavelength crosstalk. The results indicate that the synergistic effect of nonequilibrium carrier extraction at the heterojunction and electric field redistribution induced by the wide-bandgap barrier layer enables simultaneous dark-current suppression and high quantum efficiency retention in HgCdTe MWIR detectors. These simulation results not only provide physically interpretable structural design guidelines for low-dark-current and high-quantum-efficiency HgCdTe MWIR detectors, but also offer useful guidance for future experimental optimization of key factors such as composition distribution, doping concentration, heterointerface quality, and surface recombination.</p>