Tunable dielectric properties and impedance spectroscopy analysis of Au/PVA:(CoFe2O4–rGO)/n–Si structures over a wide frequency and voltage range

Abstract This study comprehensively examines voltage/frequency-dependent complex dielectric ( ε * ) behaviors, electric-modulus (M * ), ac conductivity ( σ ac ), Nyquist-diagram in the Au/PVA:(CoFe 2 O 4 – rGO)/n–Si structures by using impedance spectroscopy (IS) measurements in the wide-range (0.3 kHz–3 MHz) and voltage (− 2.0 V/ + 3.0 V). Through a comprehensive dielectric-voltage-frequency analysis, three distinct operational regions are identified: (i) the reverse bias region (− 2.0 V ≤ V ≤ − 0.4 V) shows notably low and frequency-independent real dielectric ( ε ′) below 30, indicative of limited-charge carrier dynamics within extended depletion layers; (ii) the depletion region (− 0.4 V ≤ V ≤ + 0.4 V) stabilizes ε ′ between 10 and 15, providing a consistent baseline for semiconductor parameter extraction; and (iii) the forward bias region (0.0 V ≤ V ≤ 3.0 V) reveals an extraordinary dielectric enhancement, with ε ′ reaching 140 at 0.3 kHz, attributed to interface trap ( N it ) charging and orientational polarization of CoFe 2 O 4 nanoparticles. A characteristic dielectric relaxation at 3.0 kHz produces bell-shaped imaginary-dielectric ( ε ″) peaks alongside a significant loss tangent (tanδ) of 140 at 0 V. Analysis of the real/imaginary electrical modulus (M′, M″) indicates distributed relaxation processes dominated by Maxwell–Wagner (MW) interfacial polarization, with peak M″ values between 0.28 and 0.30 under strong forward bias. AC conductivity ( σ ac ) exhibits a substantial exponential increase, attaining 0.09 S/m at 3 MHz representing nearly a two-order magnitude rise. Impedance-spectra reveal a systematic transition from capacitance-dominated behavior (~ 17 k Ω ) to a compressed resistive response (< 1 k Ω ). The voltage-tunable dielectric properties of the interlayer, governed by bias-dependent charge injection and N it activation, highlight its remarkable potential for next-generation adaptive electronic-devices requiring dynamic dielectric modulation.