Optoelectronic Synapse Behaviors of HfS<sub>2</sub> Grown via Molten Salt Flux Method

Abstract

Layered two-dimensional materials are promising candidates for next-generation semiconductor platforms owing to their atomically thin bodies, and it is crucial to develop a method for their large-scale synthesis for integrating these materials into the fabrication process. Here, we report the synthesis of a centimeter-scale HfS2 ingot using the molten salt flux method (MSFM). The structure, crystallinity, and uniformity of the synthesized HfS2 sample were verified using X-ray diffraction and Raman spectroscopy. The chemical properties were investigated using X-ray photoelectron spectroscopy. A HfS2 synaptic field effect transistor (FET) was fabricated to confirm its electrical uniformity and semiconducting nature, with an average mobility of 10.6 cm(2) V-1 s(-1). The synaptic plasticity of the HfS2 synaptic FET was investigated by applying light pulses (405 nm) in different modulation configurations. Paired-pulse facilitation was achieved by applying a continuous light pulse with a negative gate bias voltage. The modulation of synaptic weight was demonstrated under different stimulation conditions, which emulates the human brain. Furthermore, the linearity of the HfS2 synaptic device was optimized based on the frequency of the pulses to enhance learning accuracy. The approach reported here encourages the large-scaled production of transition metal dichalcogenides (TMDs) for use in artificial synaptic transistors.