Synthesis of a Selectively Nb-Doped WS2–MoS2 Lateral Heterostructure for a High-Detectivity PN Photodiode

• Published in: ACS nano 2022-08, Vol.16 (8), p.12073-12082
• Main Authors: Vu, Van Tu, Phan, Thanh Luan, Vu, Thi Thanh Huong, Park, Mi Hyang, Do, Van Dam, Bui, Viet Quoc, Kim, Kunnyun, Lee, Young Hee, Yu, Woo Jong
• Format: Article
• Language: English
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.2c02242

In this study, selective Nb doping (P-type) at the WS2 layer in a WS2–MoS2 lateral heterostructure via a chemical vapor deposition (CVD) method using a solution-phase precursor containing W, Mo, and Nb atoms is proposed. The different chemical activity reactivity (MoO3 > WO3 > Nb2O5) enable the separation of the growth temperature of intrinsic MoS2 to 700 °C (first grown inner layer) and Nb-doped WS2 to 800 °C (second grown outer layer). By controlling the Nb/(W+Nb) molar ratio in the solution precursor, the hole carrier density in the p-type WS2 layer is selectively controlled from approximately 1.87 × 107/cm2 at 1.5 at.% Nb to approximately 1.16 × 1013/cm2 at 8.1 at.% Nb, while the electron carrier density in n-type MoS2 shows negligible change with variation of the Nb molar ratio. As a result, the electrical behavior of the WS2–MoS2 heterostructure transforms from the N–N junction (0 at.% Nb) to the P–N junction (4.5 at.% Nb) and the P–N tunnel junction (8.1 at.% Nb). The band-to-band tunneling at the P–N tunnel junction (8.1 at.% Nb) is eliminated by applying negative gate bias, resulting in a maximum rectification ratio (105) and a minimum channel resistance (108 Ω). With this optimized photodiode (8.1 at.% Nb at V g = −30 V), an I photo/I dark ratio of 6000 and a detectivity of 1.1 × 1014 Jones are achieved, which are approximately 20 and 3 times higher, respectively, than the previously reported highest values for CVD-grown transition-metal dichalcogenide P–N junctions.