Cu ₂ O/WO ₃ Interfaces Designed as Terahertz/Microwave Waveguides, Negative Conductance Sources, and Mmwave Antennas

Cu 2 O, WO 3 , and Cu 2 O/WO 3 (CW) thin films were deposited by the thermal evaporation technique and studied to evaluate their structural, optical, and electromagnetic properties. X‐ray diffraction revealed amorphous phases, while scanning electron microscopy confirmed uniform surface morphology of the films. Optical analysis showed that Cu 2 O and WO 3 possess bandgaps of 2.15 and 3.38 eV, respectively, whereas the CW interfaces exhibited a reduced bandgap of 1.65 eV, indicating interfacial electronic coupling and defect‐mediated band‐tailing. The CW bilayers also demonstrated enhanced visible‐light absorption compared to single oxide films. Dielectric, optical conduction, and terahertz analyses confirmed high polarization strength and broad frequency response for CW interfaces. The Drude–Lorentz analyses confirmed the suitability of the CW interfaces as terahertz band filters. In addition, electrically, the impedance spectroscopy studies of the planar CW waveguides showed the dominant negative conductance effect in the microwave frequency domain (0.0–1.80 GHz) with a cutoff frequency exceeding 1.0 THz. Moreover, as a planar antenna, the electromagnetic characterization in the 1.0k–6.0 GHz frequency range revealed excellent impedance matching and strong microwave absorption (return loss 48.45 dB), attributed to the combined effects of interfacial polarization and conduction loss. These results confirm that CW heterojunctions are promising bilayers for optoelectronics, terahertz technology, and mmwave applications.