Enhanced photoresponse in 2D seamless metal–semiconductor contact photodiodes via one-step sulfurization synthesis

Abstract

Two-dimensional (2D) seamless metal–semiconductor contacts can significantly reduce the charge transport barrier in electronic switching devices by minimizing metal-induced defect states and eliminating dangling bonds. This approach outperforms conventional top contact and van der Waals (vdW) contact devices. However, the fabrication of a laterally connected 2D metal–semiconductor for photonic devices is highly complex and has been rarely studied. In this study, we demonstrate a high photoresponse and fast switching characteristics in a Mo_xNb_1−xS₂/n-MoS₂/p-Si/Au stacked photodiode with a 2D seamless metal (Mo_xNb_1−xS₂)–semiconductor (MoS₂) junction. This junction, formed by a one-step H₂S sulfurization process of pre-deposited Nb₂O₅/MoO₃ precursor films, allows for efficient synthesis. The 2D seamless contact-based diode exhibits excellent rectifying electrical properties, including a high forward current and a relatively low ideality factor of 2.61, outperforming those of photodiodes with conventional Au metal electrodes. It exhibited a high photo-responsivity of 2.1 A W⁻¹ and a specific detectivity of 1.55 × 10¹² Jones at −5 V under 530 nm illumination. Moreover, the device demonstrated reliable and fast switching dynamics, with a rise and fall time of approximately 17 ms at 850 nm. The high power-law exponent (∼0.89) suggests that the lateral covalent bonding between the alloyed Mo_xNb_1−xS₂ metallic layer and the MoS₂ activation layer ensures efficient transport of photo-generated charge carriers, leading to a relatively low Schottky barrier height without a vdW tunneling gap. This simple and efficient creation of a smooth 2D metal–semiconductor junction paves the way for reproducible and fast photoelectronics.