Spin PN Junctions: Giant Magnetoresistance, Tunable Circular Polarization, and Spin Zener Filter

Abstract: We demonstrate that spin PN junctions-magnetic semiconductor homojunctions with spin splitting-induced band offsets-fundamentally redefine carrier transport via spin-dependent recom bination probabilities. By integrating this mechanism into the Shockley model, we predict a near 100 enhancement in magnetoresistance sensitivity under small forward bias, where exponen tial modulation of recombination lifetimes by magnetic fields amplifies resistance changes. Angular momentum conservation enables magnetically tunable circularly polarized luminescence: exclusive conduction-band or valence-band splitting in both neutral regions achieves near-half po larization, while global splitting degrades emission coherence. Furthermore, we propose a "spin Zener filter" exploiting 1eV valence band splitting in (Ga, Mn)As, where spin-dependent barrier heights generate near 100% spin-polarized tunneling currents within a voltage-selective win dow. These results establish spin PN junctions as a universal design paradigm for magnetically amplified electronics, polarization-programmable optoelectronics, and voltage-gated spin injection without ferromagnetic contacts.