Development of Self-Doped Monolayered 2D MoS₂ for Enhanced Photoresponsivity

Transition metal dichalcogenides (TMDs) exist in two distinct phases: the thermodynamically stable trigonal prismatic (2H) and the metastable octahedral (1T) phase. Phase engineering has emerged as a potent technique for enhancing the performance of TMDs in optoelectronics applications. Nevertheless, understanding the mechanism of phase transition in TMDs and achieving large-area synthesis of phase-controlled TMDs continue to pose significant challenges. This study presents the synthesis of large-area monolayered 2H-MoS₂ and mixed-phase 1T/2H-MoS₂ by controlling the growth temperature in the chemical vapor deposition (CVD) method without use of a catalyst. The field-effect transistors (FETs) devices fabricated with 1T/2H-MoS₂ mixed-phase show an on/off ratio of 10⁷. Photo response devices fabricated with 1T/2H-MoS₂ mixed-phase show ≈55 times enhancement in responsivity (from 0.32 to 17.4 A W^-1) and 10² times increase in the detectivity (from 4.1 × 10¹⁰ to 2.48 × 10¹² cm Hz W^-1) compare to 2H-MoS₂. Introducing the metallic 1T phase within the 2H phase contributes additional carriers to the material, which prevents the electron-hole recombination and thereby increases the carrier density in the 1T/2H-MoS₂ mixed-phase in comparison to 2H-MoS_2. This work provides insights into the self-doping effects of 1T phase in 2H MoS₂, enabling the tuning of 2D TMDs properties for optoelectronic applications.