n-Si/p-NbSe2 heterojunctions enabling high rectification, illumination-controlled negative capacitance and microwave resonance with 5G/6G-band wideband matching

A vertical Au/n-Si/p-NbSe₂/Ag heterostructure was fabricated by integrating a p-NbSe₂ layer on n- Si and defining top/bottom metal electrodes to form a compact Schottky stack. X-ray diffraction failed to confirm the crystallinity of the NbSe₂ phase and the structural integrity of the junction, while scanning electron microscopy verified uniform morphology. An optically reconfigurable photocapacitive response was obtained at 1 MHz, where capacitance increased systematically with light power across the full bias range and enabled reliable extraction of junction parameters. Under illumination, the effective built-in field was reduced and the space-charge density decreased slightly, consistent with photocarrier injection and interfacial screening, while the depletion region remained sub-micron with weak power dependence. In the microwave regime, a sharp capacitance resonance near 1.2 GHz was observed, with strong tunability of amplitude and lineshape by both bias and light, including a pronounced negative-capacitance feature in a narrow band. Vector-network-analyzer measurements revealed deep impedance matching at 3.5 GHz and a broad return-loss-compliant window extending from 2.35 to 5.0 GHz, highlighting relevance to mid-band 5G/6G front-ends. Direct-current transports exhibited strong diode-like asymmetry with rectification ratios up to 10⁵. The multi-functionality of the device as a promising element for 5G/6G technology was demonstrated by combining illumination-tunable capacitance, programmable microwave resonance/negative capacitance, wideband matching, and rectifying transport in a single device.