Low-Temperature Growth of 2D-MoS₂ Thin Films by Plasma-Enhanced Atomic Layer Deposition Using a New Molybdenum Precursor and Applicability to Gas Sensors

Abstract

Two-dimensional transition-metal dichalcogenides (2D TMDs) such as molybdenum disulfide (MoS2) have received great attention for various applications. However, large-scale synthesis of high-quality 2D TMDs remains a challenge. Atomic layer deposition (ALD) is a promising deposition method for synthesizing large-area 2D TMDs, but it shows poor film quality due to the narrow process temperature window caused by the low thermal stability of conventional precursors. In this study, a plasma-enhanced atomic layer deposition (PEALD) process utilizing a new cyclopentadienyl-based Mo precursor (r-cyclopentadienyl dicarbonyl nitrosyl molybdenum, IM-02) was presented for synthesizing crystalline MoS2 at a low growth temperature. IM-02 exhibited excellent thermal stability and suitability as an ALD precursor. The resulting MoS2 thin films showed good uniformity and crystallinity without additional thermal treatment. Interestingly, the quality of the MoS2 film was further improved by exposure to H2S plasma, which increased crystallinity and reduced grain boundaries and surface defects, suppressing surface contamination by carbon and oxygen in air. The resulting MoS2 thin films were highly selective for NO2 gas, with a response rate of about 50% at 100 ppm NO2 even at room temperature, indicating their potential for use in gas sensors. These results suggest the PEALD process using IM-02 and H2S plasma as a promising approach for synthesizing high-quality MoS2 thin films, with potential applications in various fields.