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In the era of big data, negative differential resistance (NDR) devices have attracted significant attention as a means of handling massive amounts of information. While 2D materials have been used to achieve NDR behavior, their intrinsic material characteristics have produced limited performance improvements. In this article, a facile phase modification method is presented via a plasma‐assisted sulfidation process to synthesize multiphased WS2 thin films, including distorted 1 T (D‐1 T) phase and 2 H phases for photoreactive NDR devices with p‐Si. The D‐1 T phase offers a feasible route to achieve high‐performance NDR devices with excellent stability and semimetallic properties. A comprehensive investigation of experimental and computational analyses elucidates the phase transition mechanism with various temperatures and electrical properties of D‐1 T WS2. In addition, optimizing electron tunneling in the multiple‐phased tungsten disulfide (MP‐WS2)/p‐Si heterojunction at MP‐WS2 with 77.4% D‐1 T phase results in superior NDR performance with a peak‐to‐valley current ratio of 13.8 and reliable photoreactive random‐access memory. This unique phase engineering process via plasma‐assisted sulfidation provides a pioneering perspective in functionalization and reliability for next‐generation nanoelectronics.

In the past decades, toxic gas emissions have increased significantly owing to the rapid growth of industry and road transportation. Therefore, monitoring major pollutants, such as NO2, is crucial to protecting human health. The 2D materials that contain numerous adsorption sites and exhibit ultrahigh chemical reactivity can be used as sensor materials to detect these toxic gases. Herein, highly uniform, large‐area carbon‐incorporating hierarchical MoS2 nanobranches are synthesized by metal–organic chemical vapor deposition (MOCVD). An in situ carbon‐incorporation method that uses the carbon impurity present in the precursor as the seed during the MOCVD process is employed to form a hierarchical structure containing abundant adsorption sites. A gas sensor based on the resulting C‐MoS2 nanobranches contains many edge sites exhibits high adsorption energy, and consequently, has high NO2 gas sensitivity. Hence, this hierarchical C‐MoS2 gas sensor shows excellent sensing properties, exhibiting a device response of 1.67 at an extremely low NO2 concentration (≈5 ppb). The limit of detection of the gas sensor for NO2 is calculated to be low (≈1.58 ppt), further confirming its exceptional performance. Thus, the hierarchical C‐MoS2 nanobranches deposited herein provide novel insights regarding the properties of 2D materials and are highly suited for fabricating high‐performance NO2 sensors.