Tamm plasmons (TPs) can be applied in photodetector design because of the enhancement of the optical field at a specific frequency in multilayer thin films. TPs can be obtained at the interface of a metal film and distributed Bragg Reflector (DBR) and can be viewed as a degenerate case of an asymmetric metal-dielectric cavity mode. TPs can be excited under normal conditions. This plasmon appears at the interface, where the refractive index of the material changes periodically, and has the same coupling effect under transverse magnetic (TM) and transverse electric (TE) modes. The localized feature of the TPs makes them detectable only under a metal film and within a few cycles of DBR. By applying the Tamm plasmon effect, the optical field can be strongly coupled locally at the interface, significantly improving the absorptivity of the thin-film structure. Many perfect optical absorbers in the visible and near-infrared bands have been proposed, along with a lack of relevant work on DBR structures using conductive materials, which makes it difficult to fabricate photoelectric sensors using TP theory in structural design. The purpose of this study is to design an Ag-DBR structure containing an indium tin oxid(ITO) material that can produce TPs in the visible range. A new method for tuning the absorption of the structure is also proposed.

In this study, the COMSOL Multiphysics software is used to design a new composite film structure composed of metal silver and distributed Bragg grating stacked with ITO and SO₂. To construct the DBR structure, the thicknesses of the ITO layer and SiO₂ layer are set as 210 nm and 276 nm, respectively. The ITO film material used is In₂O₃-SnO₂. The physical field of the Ag thin film is constructed using the Drude model, while the contact surface between metal Ag and DBR is set by the ITO surface. Based on the transmission matrix method, the boundary condition of TP formation is established to analyze the tunability of the TPs.

As shown in Fig. 2, 559.6 nm is confirmed to represent the optical Tamm state intrinsic wavelength of the Ag-DBR composite thin film structure. Figure 3 shows the absorption curves obtained by simulation under different metal layer thicknesses. Because the silver film has strong electron absorption, when the thickness of the Ag film increases to over 54 nm, the Ag-DBR structure exhibits only the intrinsic optical properties of the silver film superimposed on the DBR. Among the different structural variants, the structure with the absorptivity of >94% and the highest edge-mode rejection ratio is selected to calculate the electromagnetic wave distribution in the multilayer film through a fluctuating optical physical field. Figure 5 shows the penetration depths of the TPs. When the metal side is in the incident plane, the TP-coupled light field can penetrate approximately four DBR structural cycles. With an increase in the DBR structure period, the penetration depth slightly increases; however, the intrinsic wavelength and peak absorptivity of the TPs do not change. When the DBR structure period is reduced to four cycles, the edge-mode rejection ratio increases sharply, and the Tamm plasmon effect decreases significantly. As shown in Fig. 6, when the thickness of the contact layer increases, the intrinsic wavelength of the TPs redshifts, and when the thickness of the contact layer decreases, the intrinsic wavelength of the TPs redshifts until the coupling fails. It can be inferred that when the variation range is ±30% of the DBR default contact layer thickness, the intrinsic wavelength of TP can be adjusted by ±15 nm with the reflectivity of less than 1%. By comparing the peak fitting curve and the DBR spectrum, it is found that the adjustable range of the TPs does not exceed the main absorption peak range of the DBR.

The absorptivity peak of the TP can be regulated in the range of 527‒560 nm by adjusting the absorption characteristics of the structure and changing the thickness of its contact layer. An Ag-DBR thin-film structure is designed and simulated using the COMSOL Multiphysics software. Based on the confirmation of the absorption peak arising from the coupling effect of the TPs, a control method with relatively simple process requirements is proposed. Tuning only requires adjustment of the thickness of the contact layer between the DBR and Ag film. The regulation range of the TP peak in the Ag-ITO composite DBR structure is 527‒560 nm, and the peak absorptivity of the structure exceeds 97% after regulation and optimization. Using this structure may simplify the design of the photoelectric conversion part in the circuit design, reduce the size of the detector, and provide a new idea for the design of next-generation photodetectors.