2D material-based heterostructures often prepared by wet transfer technique suffers from poor interface and contamination issues and it results in inferior device performance. Herein, we report an in situ chemical vapor deposition (CVD) growth of MoS2@TiO2 core-shell heterojunction with single-layer MoS2 (1L-MoS2) as the shell and 3D TiO2 nanoflower (NF) as the core for multifunctional optoelectronic applications. We explore a powerful approach to switch the trions in 1L-MoS2 into neutral excitons by developing a core-shell heterostructure with TiO2 and demonstrate a giant photoluminescence (PL) enhancement in the 1L-MoS2 shell. 3D TiO2 NFs with average diameter ∼1 μm are uniformly coated with 1L-MoS2 shell by in situ CVD technique, resulting in ∼83- and ∼30-fold enhancement in PL intensity at room temperature from the 1L-MoS2 shell on TiO2 NFs as compared to that of 1L-MoS2 grown on Ti and sapphire substrate, respectively. This high PL enhancement is attributed to the migration of excess electrons from MoS2 to TiO2, leading to a heavy p-doping in the MoS2 lattice, as evidenced by the Raman and X-ray photoelectron spectroscopy analyses. Additionally, the formation of the core-shell heterojunction facilitates the suppression of nonradiative recombination of the excitons even at the room temperature, as revealed from the low-temperature PL study. The charge transfer-induced p-doping effect in 1L-MoS2 is verified from the oxygen plasma treatment of the 1L-MoS2@Ti and it shows similar PL enhancement. Further, the 1L-MoS2@TiO2 p-n heterojunction is demonstrated as a high-performance broadband photodetector owing to its favorable band alignment and high absorption in the spectral range of 300-900 nm. The heterojunction photodetector exhibits a record high responsivity and detectivity of ∼35.9 A W-1 and 1.98 × 1013 jones, respectively, in the UV region, and ∼18.5 A W-1 and 1.09 × 1013 jones, respectively, in the visible region. As compared to the 1L-MoS2@Ti and 1L-MoS2@SiO2 with slow photoresponse, 1L-MoS2@TiO2 heterojunction exhibits more than 1 order of magnitude faster photoresponse (rise/fall time ∼33.7/28.2 ms), which is attributed to the fast photogenerated carrier transport at the p-n heterojunction due to the large built-in electric field. This high-performance 1L-MoS2@TiO2 core-shell heterojunction grown by a novel in situ CVD technique is promising for the cutting-edge optoelectronic applications.
Keywords: MoS2 doping; MoS2@TiO2 heterojunction; broadband photodetection; excitonic photoluminescence; fast photoresponse; in situ CVD growth.