Investigation of the transient photo-response and switching window of an Al/indigo/Al device: unveiling negative photoconductivity and the photo-enhanced memory window

Abstract

Memristors have redefined the technological horizon by seamlessly intertwining memory storage, data processing and sensing techniques such as light sensing within a single unit. We investigated the impact of UV (375 nm) and blue light (475 nm) on a memristor based on a natural dye, indigo (C₁₆N₁₀H₂O₂). Our findings indicate that the device exhibits higher sensitivity to UV light and shows negative photoconductivity (NPC) for both light sources when illuminated independently. DC current–voltage measurements show that there is drastic reduction in the current under UV light illumination compared to current–voltage measurements done in the dark. The reduction in the current when exposed to UV and blue light is attributed to the capture of the carriers by the defects present in the indigo film. Deep trap energy levels (0.35–0.5 eV) are found to be responsible for the carrier capture. Upon exposure to constant intensity, a combined positive and negative photoconductive effect is seen. This effect arises due to competition between electron–hole pair generation and the carrier capture by defects. Furthermore, highly stable resistance states with a memory window of 1.8 MΩ in the dark and an enhanced memory window of 3.39 MΩ under UV light are obtained. In our study, we have established a highly stable resistive switching device with a photo-enhanced memory window under UV illumination. The possibility of combining photodetection, data processing, data storage and photo-enhanced data storage in a single cell is demonstrated in this work.