Engineering the interface of schottky diodes with a pva:(CoFe ₂ O ₄ -rGO) nanocomposite for enhanced frequency response via admittance spectroscopy

This study examines the frequency- and voltage-dependent electrical parameters, interface trap densities (D it ), and relaxation times (τ) in Au/PVA:(CoFe 2 O 4 -rGO)/n-Si structures using three complementary admittance methods. CoFe2O4 nanoparticles, synthesized hydrothermally, were incorporated with reduced graphene oxide (rGO) into polyvinyl alcohol (PVA) matrices and spincoated onto n-Si substrates to form interfacial layers. Capacitance-voltage (C-V) and conductancevoltage (G/ω-V) measurements spanned -2.0 V to +3.0 V across 0.3 kHz - 3 MHz. Pronounced frequency dispersion was observed: forward-bias capacitance at +3.0 V fell from ~9 nF (0.3 kHz) to ~2.5 nF (3 MHz), while the normalized conductance peaked near 0.8-1.0 V at all frequencies, with trap saturation above ~0.75 V. Hill-Coleman analysis revealed Dit values that decline quasiexponentially from ~1.3 × 10 14 eV -1 cm -2 at low frequencies to ~1.0 × 10 13 eV -1 cm -2 at high frequencies. Parallel-conductance extraction revealed τ spanning three orders of magnitude, from ~120 µs at 0.20 V to ~0.08 µs at 1.60 V, with the normalized conductance saturating above ~0.75 V, consistent with strong field-induced acceleration of trap dynamics and near-complete filling of accessible trap levels under moderate forward bias. This behavior arises because the AC period shortens relative to τ: once the period falls below the trap response time, slower states cease contributing to the measured admittance. The apparent donor concentration decreased from ~2.15 × 10 17 cm -3 to ~7.7 × 10 15 cm -3 over the same frequency range, while the depletion width expanded from ~6.6 µm to ~39.9 µm, and the peak electric field diminished from ~2.17 × 10 5 V/cm to ~4.75 × 10 4 V/cm over the same frequency range, and the peak electric field decreased from ~2.17 × 10 5 V/cm to ~4.75 × 10 4 V/cm over the same range. Unlike conventional low-dielectric interlayers that cannot fully suppress interface states or reduce series resistance, the high-dielectric PVA:(CoFe 2 O 4 -rGO) nanocomposite studied here offers a broader operating window by neutralizing a substantial fraction of Nss while regulating charge transport mechanisms. To our knowledge, this is the first frequency-resolved, multi-method mapping of D it and τ distributions in such a system, offering practical guidance for engineering nanocomposite interlayers with tailored trap spectra.