Conformal Growth of Nano-Patterned Monolayer MoS2 with Periodic Strain via Patterned Substrate Engineering for High-performance Photodetectors

Abstract

The extraordinary mechanical compliance of 2D molybdenum disulfide (MoS₂) makes it an ideal candidate for strain modulation of various electrical and optical properties. However, developing facile methods for accurate and stable engineering of strain still remains a major challenge. Here, a novel and effective method is demonstrated for introducing periodic strain into monolayer MoS₂ by direct growth on nano-patterned sapphire substrates (NPSS). A mixed aqueous solution of Na₂MoO₄ and NaOH is spin-coated on the NPSS and sulfurated in one step by chemical vapor deposition (CVD). Highly oriented monolayer MoS₂ single-crystal nanosheets with high quality and few sulfur vacancies are achieved conformally on the NPSS via a liquid-mediated growth mode. Notably, the periodically distributed blue shift of the PL emission peak demonstrated periodic compressive strain is introduced into the nano-patterned MoS₂ via the thermal expansion difference between MoS₂ and substrates. Furthermore, photodetectors fabricated using the nano-patterned monolayer MoS₂ exhibit a high photo-to-dark current ratio (PDCR) over 10⁶, an excellent detectivity of 5.4 × 10¹³ Jones, and a fast photoresponse of 7.7 ms, owing to the strain-induced back-to-back built-in electric field, enhanced light absorption by light-scattering effect and fewer S vacancy defects. The scanning imaging demonstration based on the single-pixel nano-patterned MoS₂ photodetector further confirms its great potential in image sensors. This work hereby presents a pathway for direct conformal growth of nano-patterned monolayer MoS₂ with precisely periodic strain, which should inspire the applications for high-performance optoelectronic devices via the strategy of patterned substrate engineering by the periodic nanostructures.