Previously, it was established that the optimal anodizing current density for producing PS corresponding to LPE is 0.02 mA/cm². (30) This work prepared PS samples under the parameters and further investigated them. Figure 2a,b illustrates the variations in LPV and sensitivity of MoS₂-GF/PS/p-Si irradiated by a 520 nm laser with different PS anodizing times. Initially, the structure exhibits high sensitivity without anodizing, which decreases significantly over time, peaks at 30 min with an ultrahigh sensitivity of 1195.02 mV/mm, and subsequently declines again. Figure 2c,d depicts the LPV and sensitivity changes of MoS₂-GF/PS/p-Si with varying thicknesses of MoS₂-GF. Comparing these with those in Figure 2a, it is evident that the sensitivity of PS/p-Si is markedly lower than that of MoS₂/p-Si. Upon sputtering MoS₂ onto PS/p-Si, the LPE is significantly enhanced. However, with increasing MoS₂-GF thickness, the sensitivity initially decreases, then rises again, likely influenced by sputtering dynamics and the narrow band gap of MoS₂. This enhancement primarily arises from the increased concentration of photogenerated charge carriers within the MoS₂. However, at a thickness of 10.764 nm, the sensitivity decreases again and stabilizes. This decline can be attributed to the formation of a continuous, smooth MoS₂ film, transitioning from a granular structure. Consequently, the surface of PS becomes predominantly covered by the MoS₂ layer, adversely affecting its light absorption characteristics.

LPE is also influenced by wavelength variations. Figure 2e,f depicts the LPV and sensitivity of MoS₂-GF/PS/p-Si at different laser wavelengths. The structure exhibits exceptionally high sensitivity at shorter wavelengths: 855.94 mV/mm at 405 nm and 1195.02 mV/mm at 520 nm. However, sensitivity decreases to 554.03 mV/mm at 635 nm and then increases again to 877.14 mV/mm at 780 nm, stabilizing near 450 mV/mm in the near-infrared band, different from our previous study. (30)

Quantum dots, as low-dimensional semiconductor materials, have garnered significant attention in recent years. (21,23,32) Therefore, we replaced MoS₂-GF with MoS₂-QDs to further investigate their distinct manifestations and mechanisms in the LPE. Figure 2g,h illustrates the LPE of MoS₂-QDs/PS/p-Si. Surprisingly, MoS₂-QDs/PS/p-Si also exhibited notable photovoltaic effects. Under 520 nm laser irradiation, the sensitivity reached 951.71 mV/mm. The structure maintains a sensitivity of over 350 mV/mm across the visible spectrum. However, the sensitivity in the 980 nm near-infrared band is lower at 199.54 mV/mm, representing a significant improvement compared to other structural types.

Both MoS₂-GF/PS/p-Si and MoS₂-QDs/PS/p-Si structures surpass that reported in other studies by several orders of magnitude, as shown in Table 1. This finding is particularly remarkable and represents a surprising discovery not previously reported in related studies. The MoS₂-GF/PS/p-Si composite demonstrates outstanding sensitivity across a broad spectrum from the visible to near-infrared wavelengths. Even in the 980 nm near-infrared band, it maintains a sensitivity of 435.6 mV/mm, surpassing that of most near-infrared photodetectors. The LPE nonlinearity (33) of both structures was calculated to be less than 1% (Supporting Information Table S1), indicating that LPV exhibits a superior linear correlation with the laser position. These results highlight this study’s exceptional performance and practical significance, positioning it as an innovative candidate for the advancement of broadband detection systems. (34)

Figure 3a depicts the PL spectra of PS/p-Si, MoS₂-QDs/PS/p-Si, and MoS₂-GF/PS/p-Si excited by a 320 nm laser. PS/p-Si exhibits strong PL, (41) emitting photons at a rate 10–100 times higher than MoS₂-QDs/PS/p-Si and MoS₂-GF/PS/p-Si structures, consistent with Figure 1c. This suggests that a significant portion of LPV observed in MoS₂-QDs/PS/p-Si and MoS₂-GF/PS/p-Si structures is due to the reduced PL phenomena, thereby minimizing the recombination of photogenerated charge carriers with holes. The inset in Figure 3a compares the PL intensities of MoS₂-QDs/PS/p-Si and MoS₂-GF/PS/p-Si. MoS₂-QDs/PS/p-Si exhibits a weaker emission peak at 452 nm, consistent with the PL emission peak of MoS₂-QDs, resulting in a lower sensitivity at 405 nm (42) (Figure 2h). Both structures show an emission peak near 609 nm, corresponding to the sensitivity trough observed in the “M”-shaped variation with wavelength. Unlike PS/p-Si, MoS₂-GF/PS/p-Si and MoS₂-QDs/PS/p-Si exhibit a PL spectrum with distinct multiple emission peaks. The corresponding wavelengths of emission peaks can be obtained by fitting these peaks with the Lorentz function, as shown in Figure 3b,c. When excited at a wavelength of 677 nm, MoS₂-GF/PS/p-Si shows blue-shifted emission peaks at 437, 451, 467, and 553 nm. Meanwhile, MoS₂-QDs/PS/p-Si exhibits emission peaks at 389, 460, 542, and 612 nm. The cumulative fitting curve closely matches the experimental data. The blue-shifted peaks of these two structures exhibit similar distribution characteristics but also show distinct differences. Therefore, in this study, the Blueshift affects the response of the different structures to the optical wavelength band, which, in turn, assists the generation of photogenerated carriers.

Figure 3a illustrates a strong PL phenomenon in PS, as depicted schematically in Figure 4a. Electrons in PS are excited by a laser, separating from holes and transitioning to the CB. However, these photoelectrons readily recombine with holes, emitting photons simultaneously, which constitutes the PL phenomenon. In terms of LPE, such recombination significantly reduces the carrier density within the structure, which is detrimental to achieving high LPV and sensitivity. Therefore, the PL phenomenon is greatly weakened by sputtering MoS₂-GF and spinning MoS₂-QDs on the PS surface in this work.

MoS₂, as a narrow-band-gap semiconductor (1.2–1.9 eV (48)), exhibits n-type semiconductor characteristics, primarily attributed to sulfur vacancies, and offers significant advantages in enhancing light absorption. Upon contact with PS, a heterojunction forms, forming a depletion region, as illustrated in Figure 4c. When exposed to a laser, MoS₂ and PS generate abundant photogenerated carriers. Concurrently, the barrier height decreases, allowing more photogenerated carriers to diffuse across the junction into the PS, thereby enhancing light absorption. The formation of heterojunctions promotes carrier diffusion and reduces the level of recombination of photogenerated carriers with holes, thereby attenuating the photoluminescence phenomenon. Figure 4b illustrates the schematic model of the photoexcited electron-motion profile in the MoS₂-GF/PS/p-Si structure. At the illumination spot, electrons and holes separate and drift in opposite directions. Photogenerated electrons from PS and MoS₂-GF contribute to establishing a lateral density gradient extending from the irradiated to the nonirradiated regions. This gradient stabilizes until the distribution of photogenerated electrons forms a steady lateral concentration difference.

As for MoS₂-QDs, the quantum confinement effect in quantum dots, due to their size reduction, widens the band gap of MoS₂. (49) Consequently, it becomes more challenging to generate numerous photogenerated carriers in MoS₂-QDs under excitation in the visible or near-infrared spectrum compared to that in MoS₂ alone. In fields like solar cells and light detectors, quantum dots are pivotal in enhancing light absorption and sensitization. Quantum dots act as catalysts or light-trapping cells, mediating carriers. (32,50,51) Figure 4d illustrates a schematic diagram of photogenerated charge carrier generation and recombination in MoS₂-QDs/PS/p-Si. Considering the photocatalytic mechanism of quantum dots, they likely serve an additional role on the PS/p-Si surface as photogenerated carrier mediators. Laser illumination induces photoexcitation of electrons in the PS, causing them to transition from the VB to the C, while simultaneously generating holes in the VB. Due to the lower Fermi level of the quantum dots, the excited photogenerated electrons are effectively trapped by these QDs. This depletion of electron density in the CB reduces the likelihood of electron–hole recombination, leading to a decrease in the PL intensity emitted by the structure. As the photogenerated charge carriers migrate, trapped electrons on the QDs return to the PS, thereby enhancing the efficiency of photogenerated electron utilization. The light absorption rate shown in Figure 5d further supports the carrier-mediated role of quantum dots, a concept that will be elaborated on later.

The MoS₂ on the PS surface appears as a granular film rather than a continuous film. Under optimal LPE conditions, the nominal thickness of MoS₂-GF is 1.196 nm, allowing the nanoparticles to infiltrate the PS pores. This configuration serves two primary purposes: first, it facilitates the formation of multidirectional heterojunctions within the pores, and second, it significantly enhances the carrier diffusion length to compensate for the presence of PS pores. Figure 5a–c presents carrier diffusion length fitting curves for PS/p-Si, MoS₂-GF/PS/p-Si, and MoS₂-QDs/PS/p-Si structures, respectively. According to the basic theory of LPE, the LPV is related to the electron diffusion length λ_s and electron–hole pair density N at the laser position x by the form $\mathrm{LPV}\propto N\left[\exp \right(?\frac{|{\displaystyle \frac{L}{2}}?x|}{{\lambda }_{\mathrm{s}}})?\exp (?\frac{|{\displaystyle \frac{L}{2}}+x|}{{\lambda }_{\mathrm{s}}}\left)\right]$, (4) where L is the distance between two contact points. Therefore, a longer carrier diffusion length can contribute to a greater lateral carrier concentration gradient, which is advantageous for enhancing sensitivity. From the figures, their fitted diffusion lengths are λ₁ = 232.64 ± 19.85 μm, λ₂ = 476.18 ± 53.6 μm, and λ₃ = 465.02 ± 80.17 μm. Comparing λ₁ and λ₂, the presence of pores in PS poses significant obstacles to the migration of photogenerated carriers, resulting in smaller lateral concentration gradients. Upon sputtering MoS₂ onto the surface, both the nanoparticles in contact with PS and those entering the pores form heterojunctions, providing additional photogenerated electrons, N, and expanding λ. The sensitivity shown in Figure 2d with respect to MoS₂ thickness is also linked to the carrier diffusion length. The continuous and increasing thickness of the MoS₂ film results in a reduced resistivity and enhanced carrier diffusion length. This allows electrons to diffuse more readily from the point of illumination to the adjacent areas, leading to elevated electron concentrations near both contact points. As a result, the potential difference between the two contact points diminishes, causing the observed weakening of the LPE. MoS₂-QDs similarly contribute to the expansion of λ, but MoS₂-GF/PS/p-Si exhibits a larger diffusion length, consistent with experimental results. It can also be inferred that MoS₂ outperforms MoS₂-QDs in optimizing λ.