Ultraviolet photo-memory with image storage functions by controlling carriers' lifetime

Ultraviolet (UV) photodetectors (PDs) have been widely developed for multifunctional applications such as flame detection, space communication and missile detection etc. However, limited attention has been paid to developing UV PDs with photo-memory capabilities, despite their enormous potential for applications in the field of imitating human learning and memory. In this work, we propose a ZnS/ZnO/ZnS heterojunction for UV optoelectronic synapse with optoelectronic memory functions. Through the incorporation of a ZnS shell layer, we achieved a substantial enhancement in the near-band photoluminescence of ZnO and a marked improvement in the lifetime of photo-generated carriers. The ZnS/ZnO/ZnS-3 h UV PD demonstrate a responsivity of 3.6 A/W (5 V bias 0.28 mW/cm2 365 nm light.), which is 12 times of that of ZnO UV PD (0.3 A/W). Additionally, by controlling the thickness of ZnS shell, we extend the decay time of ZnS/ZnO/ZnS-3 h UV PD from 95 s (ZnO) to 378 s, indicating its potential for UV image storage. Also, it shows versatile synaptic functions, including photonic potentiation, paired-pulse facilitation, short-/long-term memory, as well as a "learning" behavior. These results show that UV PDs with long decay time have new potential applications in UV image storage.