Resistive Switching Accompanied by Negative Differential Resistance in Cysteine-Functionalized WS₂ Quantum Dots toward Nonvolatile Memory Devices

Coexistence of resistive switching (RS) and negative differential resistance (NDR) has attracted much attention because NDR is beneficial for the realization of multilevel storage in RS devices. However, there is no report regarding the coexistence of NDR and RS for semiconductor quantum dots (QDs), which are suitable for memory devices. Here, RS behavior with the NDR effect based on cysteine-functionalized WS2 QDs has been demonstrated. A peculiar symmetric I–V loop with unipolar switching was observed during a complete voltage sweep cycle. The NDR effect can be adjusted by varying the voltage scan rate, and a peak-to-valley ratio as high as 9.85 has been attained. A model based on tunneling transport and carrier trapping has been proposed to explain NDR behavior accompanied by RS. The reproducibility of the RS and NDR has been evaluated after 100 sweeps under ambient conditions, giving evidence of a stable and high on–off resistance ratio of ∼104. This study may initiate a feasible way to implement a nonvolatile memory device based on cysteine-functionalized WS2 QDs.