【Member Papers】Multiband bipolar photoresponse in Cu@CuOₓ@a-Ga₂O₃ core-shell heterostructure-based self-powered photoelectrochemical-type photodetector for secure underwater optical communication

Figure 1. Preparation and characterization of Cu@CuO_x@a-Ga₂O₃ network films. a) Schematic illustration of the preparation process for Cu@CuO_x@a-Ga₂O₃ network films. SEM images of Cu NWs networks b), Cu@CuO_x network film c), and Cu@CuO_x@a-Ga₂O₃ network film d). e) SEM image combined EDS elemental mapping of a single Cu@CuO_x@a-Ga₂O₃ nanowire. f) XRD spectrum, g) Raman scattering spectrum of Cu NWs film, Cu@CuO_x film and Cu@CuO_x@a-Ga₂O₃ film. h) Cu 2p XPS spectrum of Cu@CuO_x@a-Ga₂O₃. i) TEM image of Cu@CuO_x@a-Ga₂O₃. j) HRTEM image of the green boxed area in (i). k) The magnified regions (I-III) and FFT image (IV) of the corresponding color boxed areas in (i).

Figure 2. Energy band structure of CuO_x@a-Ga₂O₃. a) Ga 2p3/2 core-level spectrum and valence band spectrum of a-Ga₂O₃. b) Cu 2p3/2 core-level spectrum and valence band spectrum of Cu@CuO_x. c) Ga 2p3/2 and Cu 2p3/2 core-level spectra of Cu@CuO_x@a-Ga₂O₃. d) Absorption spectrum and optical band gap of Cu@CuO_x. e) Absorption spectrum and optical band gap of a-Ga₂O₃. f) Schematic illustration of the energy band alignment of CuO_x@a-Ga₂O₃ in the working electrode.

Figure 3. Investigation on the wavelength-induced bipolar mechanism of Cu@CuO_x@a-Ga₂O₃ PEC-BPDs with varying a-Ga₂O₃ layer thickness. a) Broad-spectrum photoelectric properties of a-Ga₂O₃ and Cu@CuO_x PEC-PDs (0 V, 0.8 mW/cm²). b) Broad-spectrum photoelectric properties of Cu@CuO_x@a-Ga₂O₃ PEC-BPD (0 V, 0.8 mW/cm²). c) I-t curves under 254 nm light irradiation and d) I-t curves under 365 nm light irradiation of Cu@CuO_x@a-Ga₂O₃ PEC-BPDs with different a-Ga₂O₃ deposition times (0 V, 0.8 mW/cm²). Band bending and charge transfer under 254 nm light irradiation for Cu@CuO_x@a-Ga₂O₃ films with thin e), medium f), and thick g) a-Ga₂O₃ layers. Band bending and charge transfer under 365 nm light irradiation for Cu@CuO_x@a-Ga₂O₃ films with thin h), medium i), and thick j) a-Ga₂O₃ layers.

Figure 4. Demonstration of reprogrammable optical switching logic gates based on Cu@CuO_x@a-Ga₂O₃ PEC-BPD with 30 min a-Ga₂O₃ sputtering time. a) Schematic diagrams of four optical switching logic gates: OR, NOT, XOR, and NAND. b) Truth table of OR, NOT, XOR, and NAND logic gates. c) Photocurrent values of Cu@CuO_x@a-Ga₂O₃ PEC-BPD by single input signals (254 or 365 nm) for different logic gates, with the light intensity and bias voltage of the two signals. I-t curves of OR d), NOT e), XOR f), and NAND g) logic gates with 254 nm and 365 nm illumination. I-t curves of OR h), NOT i), XOR j), and NAND k) logic gates with 254 nm and 520 nm illumination. The on/off states of 254 nm and 365 nm/520 nm LEDs correspond to input logic states of 1/0. For the output photocurrent within the range of -0.25~0.25 μA/cm², the output state is set as “0”, while the photocurrent outside this range indicates the output state “1”.

Figure 5. Demonstration of the encrypted optical communication system. a) Conceptual diagram of encrypted optical communication system. b) Diagram of AMI code splitting. c) The self-verification mechanism of the system when abnormal signal occurs. The bipolar photocurrent response curves of the Cu@CuO_x@a-Ga₂O₃ PEC-BPD under parallel signal transmission with combined wavelengths of 254 nm and 365 nm d), 254 nm and 520 nm e) to transmitte the information “CQNU”.

DOI：

https://doi.org/10.1016/j.cej.2025.170508