Optoelectronic Memristors Based on ZnS-Passivated CdZnSe Quantum Dots for Neuromorphic Synaptic Emulation Enabling Information Encryption
Neuromorphic computing demands energy-efficient synaptic devices that emulate biological plasticity. Optoelectronic memristors based on colloidal quantum dots (QDs) offer tunable bandgaps and solution processability, yet suffer from defect-mediated nonradiative recombination and instability. Here, we report ZnS-passivated CdZnSe core/shell QDs as the active layer in memristive devices, achieving enhanced synaptic emulation and information encryption. Time-resolved photoluminescence (TRPL) decay curves were fitted with a tri-exponential function, revealing that ZnS passivation suppresses defect-related trap states, prolonging the average carrier lifetime from 12.3 ns (CdZnSe) to 28.7 ns (CdZnSe/ZnS). The intensity proportion of the fast decay component (τ1 ≈ 1.2 ns) decreased from 45% to 18%, indicating reduced surface trapping. Devices incorporating CdZnSe/ZnS QDs exhibit stable bipolar resistive switching with an ON/OFF ratio exceeding 10^3, endurance of >10^3 cycles, and retention of >10^4 s. Under 365 nm UV illumination, the devices show light-tunable synaptic plasticity, including paired-pulse facilitation (PPF) with a facilitation index of 180% at a 50 ms interval, and transition from short-term to long-term memory. The memristors successfully emulate essential synaptic functions and are employed in a simple encryption scheme, demonstrating the potential of defect-passivated QDs for secure neuromorphic hardware.