*4.2. Device Characterization*

A photo-sensitive device was fabricated with flexible electrodes and a transparent gallium oxide film based on LM(EGaIn), as shown in Figure 4a. The black rectangular areas on the right side of the figure are the LM electrodes patterned by a fiber laser, and the transparent area is a gallium oxide film beneath the PDMS substrate. The center image in Figure 4a shows the bird's-eye view of the full structure of the device.

It is known that Ga2O3 has a wide bandgap (4.5~4.9 eV) at room temperature [46,47]. As a result, the device is used to measure ultraviolet and visible light as a high-range photodetector. As shown in Figure 4b, the characteristics show an obvious photo-responsive performance under periodic illumination. Photo-responsive tests were also performed with light of three different wavelengths. The devices were illuminated by light periodically at intervals of 30 s with three wavelengths: 254 nm, 365 nm, and visible light. The rise/decay times of the device under illumination of 254 nm, 365 nm, and visible light were 28.2 s/26.7 s, 18.3 s/21.9 s, and 29.1 s/23.6 s, respectively. The responsivities (R) under illumination of 254 nm, 365 nm, and the visible light at 1 V were 2.8 × 10−<sup>2</sup> A/W, 3.3 × 10−<sup>3</sup> A/W, and 2.6 × 10−<sup>6</sup> A/W, respectively. As shown in Figure 4c, the device based on EGaIn shows a photo-response-current ratio (ΔI/I0) of 30.3% under 254 nm ultraviolet light with an intensity of 0.1 mW/cm2. It also shows photo-response–current ratios of approximately 14.7% and 16.1% under the illumination of a 365 nm ultraviolet and an ordinary visible light, respectively.

**Figure 4.** (**a**) Images of the photodetector combined with the conductive electrode and photo-responsive film; (**b**) Time-dependent photo-response curves and (**c**) photo-response-current ratios of the photodetector under illumination with ultraviolet light (λ~254 nm and 365 nm) and visible light. The bias voltage was 0.1 V, and the on/off time of lights was 30 s/30 s.
