We propose a step-barrier diode based on a monolayered transition metal dichalcogenide that simultaneously exhibits complete valley and spin filtering and pronounced multipeak negative differential resistance (NDR) under off-resonant circularly polarized light (CPL). The NDR originates from resonant tunneling via a quantum well formed by the step barrier and forward bias. The valley selectivity of CPL makes the current valley polarized. Owing to the strong intrinsic spin-orbit coupling, this valley polarization accompanies a spin polarization with the same amplitude. Current calculated by the scattering-matrix formalism shows that tuning the barrier height can amplify the NDR magnitude and produce more current peaks. Reversing the CPL helicity or slightly adjusting the bias voltage switches the dominant transport channel between the $K$ and $K^{\mathrm{\prime }}$ valleys and related spins. This enables electrically and optically reconfigurable valley and spin filtering and NDR within a single device. The proposed device offers an experimentally accessible route toward multivalued logic and high-speed valleytronic applications.

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• Ballistic transport
• Optoelectronics
• Valleytronics
• Diodes
• Semiconductor compounds
• Transition metal dichalcogenides
• Landauer formula
• S-matrix method in transport