Amorphous to Crystalline Transition and Indium-Vacancy Mediated Synaptic Functionality With Ultralow Energy...

An optoelectronic synapse (OES) is a key component for brain-inspired computing and holds great promise towards energy-efficient computation, where energy consumption remains one of the key challenges. Herein, we report a metal (In) vacancy in Indium Selenide (In₂Se₃) that induces electronic defects owing to its transition from amorphous to crystalline γ-phase during thermal annealing. These In vacancies facilitate charge trapping and slow release, enabling persistent photoconductivity, and the corresponding OES shows a long decay time of ∼214 s. The OES also demonstrates important synaptic characteristics, for example, paired-pulse facilitation, short-term and long-term memory, synaptic plasticity, and learning-forgetting behavior. We show that due to the crystallization of In₂Se₃ film, the electrical conductivity is enhanced by ∼10⁴ times, which made it possible to realize the synaptic phenomena with a remarkably low energy consumption of ∼180 aJ per spike, well below the energy range of biological systems. Further, our device has realized an exceptional accuracy of ∼94% for the MNIST handwritten digit recognition using artificial neural network simulation, while an accuracy of $\sim$ 85% has also been realized for a U-Net structure-based network for semantic segmentation work. These findings open new pathways towards energy efficient OES for next generation neuromorphic computing and vision systems.