PbS@MoS₂ core-shell heterojunction and broadband photodetector

Broadband photodetectors that sense and process multiple spectral bands are essential for environmental monitoring, optical communications, and integrated optoelectronics, yet state-of-the-art devices still face materials constraints. Molybdenum disulfide (MoS₂), a prototypical two-dimensional transition-metal dichalcogenide, offers high carrier mobility and intrinsically low dark current, but its native photoresponse is largely confined to the visible region, which limits single-material devices in applications requiring coverage extending into the near-infrared (NIR). To overcome this spectral bottleneck while addressing long-standing issues of small interfacial area and contamination in conventional heterostructures, we developed a core-shell lead sulfide (PbS)@MoS₂ heterojunction, where MoS₂ is directly grown on PbS nanoparticles via chemical vapor deposition (CVD). This growth mode achieves conformal encapsulation and atomically clean, intimate contact over a maximized interface, enabling efficient charge transfer pathways without extraneous barriers. Structural and optical characterizations confirm uniform, continuous shells with good crystallinity and well-defined vibrational and photoluminescence (PL) signatures. In particular, Raman and steady-state PL spectroscopy reveal a slight redshift of MoS₂ excitonic emission in the core-shell configuration, which is consistent with gentle tensile strain in the curved shell and interfacial charge transfer that suppresses radiative recombination. Coupled with the built-in electric field arising from carrier diffusion at the core-shell boundary, these effects bend the bands and lower the electron injection barrier from PbS into MoS₂, thereby facilitating spatial separation and transport of photocarriers under both visible and NIR excitation. On this materials platform, we fabricated broadband photodetectors and quantified their performance. Under 532 nm illumination, the PbS@MoS₂ device delivers a responsivity of 0.88 A/W, a specific detectivity of 9.06×10¹⁰ Jones, and an external quantum efficiency (EQE) of 205.17, which demonstrates that the clean, large-area interface converts incident photons into electrical signals with high gain. Crucially, at 1050 nm, a wavelength where pristine MoS₂ is essentially non-absorbing, the same device exhibits a clear photoresponse with reproducible on/off switching. This indicates that the PbS core extends the absorption edge, while the MoS₂ shell provides a low-noise transport channel. Thus, the core-shell structure expands the operational bandwidth while preserving the low-dark-current merit inherent to MoS₂. Mechanistically, the combination of interfacial band bending, curvature-induced strain in the shell, and expanded effective contact area accounts for the reduced recombination rate and slight PL redshift observed experimentally, and directly links band-structure modulation to enhanced device figures of merit. This work establishes a scalable CVD route to PbS@MoS₂ heterojunctions with atomically clean interfaces and maximized contact area, offering a practical solution to interface contamination and area limitations that hindered earlier MoS₂-based broadband architectures. By uniting visible-to-NIR absorption, efficient interfacial charge separation, and stable transport in a single hybrid, the proposed design provides a robust pathway toward high-performance broadband photodetectors and holds strong potential for on-chip optoelectronic integration and wide-band sensing systems.