**2. Materials and Methods**

GAG multilayered structures were deposited on glass and surface-oxidized Si pieces by DC magnetron sputtering method using a Magnetron setup (Russia) equipped with two sputtering units. The base pressure of the chamber was maintained at 2 <sup>×</sup> <sup>10</sup>−<sup>4</sup> Pa.

The bottom and top oxides layers were deposited using Ga (3 at.%)-doped ZnO target under the following deposition conditions: Ar working pressure of 0.5 Pa, discharge current of 270 mA, discharge voltage of 720 V. The Ag thin interlayer was deposited using an Ag (99.99%) pure target under the following conditions: Ar working pressure of 0.5 Pa, discharge current of 150 mA, discharge voltage of 750 V. Before the formation of each layer of the GAG trilayered structure, a presputtering cycle of both GZO and Ag targets on a closed shutter was performed for 10 and 3 min, respectively. The distance between targets and substrates was 150 mm. The substrates revolved at a rate of 30 r/min. The substrate was not specially heated during the growth of multilayers, but there was a slight heating to about 50 ◦C due to ion bombardment. The growth rates for the oxide and metal components of the three-layer structure under such conditions were 1.33 and 3.00 nm/min, respectively. The thickness of oxide and metal components of the GAG multilayer was controlled by varying the deposition time, which was the same for bottom and top GZO films in order to create a symmetric trilayer structure. Layer thickness variations were also confirmed by cross-sectional scanning electron microscopy (SEM) and were consistent with the estimated depositing times (Figure S1 of Supplementary Materials (SM)).

Table 1 shows thickness data of seven multilayered samples with various geometries. For the first five samples (from GAG-0 to GAG-4), the thicknesses of the silver interlayer were varied between 0 and 12 nm, while keeping fixed thicknesses for oxide top and bottom GZO layers (40 nm). For the samples GAG-5 and GAG-6, the thickness of oxide films was varied, keeping the thickness of the Ag interlayers fixed (10 nm). For comparison, a two-layered GA with a 80-nm thick bottom oxide and thin upper metal layer (10 nm) was deposited additionally.


**Table 1.** Nomenclature of Ga-doped ZnO/Ag/Ga-doped (GZO/Ag/GZO) multilayered structures.

The surface morphologies of the deposited samples were investigated by using a Leo-1450 scanning electron microscope (SEM) (Carl Zeiss) and a Ntegra Prima atomic force microscope (NT-MDT SI). X–ray diffraction (XRD) patterns were collected on a X'PERT PRO MPD diffractometer (PANalytical) with CuKα radiation (λ = 1.5418 Å). The electrical properties were measured by using the four-probe technique (IUS-3, Russia). Optical transmittance spectra were obtained by a UV-3600 optical spectrophotometer (Shimadzu) in the wavelength range of 340–1240 nm. All of the measurements were carried out at room temperature.
