The realization of half-metallicity in two-dimensional materials is of considerable interest for the development of nanoscale spintronic devices. In this work, we systematically investigate the electronic structure and spin-dependent quantum transport properties of substitutionally Mo-doped GaSe monolayers using first-principles calculations combined with the nonequilibrium Green's function formalism. Our results show that Mo substitution induces half-metallic behavior in intrinsically nonmagnetic GaSe. Driven by strong $p\text{–}d$ hybridization and substantial on-site exchange splitting, the spin-down channel exhibits a wide energy gap of 1.65 eV, resulting in highly spin-selective transport. Within the collinear spin-conserving transport framework employed here, the calculated spin-filtering efficiency reaches 100% under all finite bias voltages within the range of $\pm 0.5\mathrm{V}$. The spin-up channel also exhibits pronounced negative differential resistance and a magnetoresistance ratio exceeding ${10}^{11}$. Real-space analysis further reveals that the spin-polarized transport is mediated by a rhombic reticular nanochannel whose bias-driven evolution from a continuous resonant network to discretized islands affects the current response. These results suggest that Mo-doped GaSe is a promising candidate for spin-filtering and related spintronic applications.

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• Doping effects
• Quantum transport
• Spin current
• Spin filtering
• Spintronics