Frequency and voltage-dependent dielectric spectroscopy characterization of Al/(Coumarin-PVA)/p-Si structures

In this study, the frequency/voltage dependence of the dielectric constant (ε′), dielectric loss (ε″), real/imaginary components of the complex electric modulus (M′, M″), tangent loss (tan δ), ac electrical conductivity (σ_ac), real and the imaginary parts of the complex impedance (Z^*), phase angle (θ) between resistance current, and capacitive current of the Al/(Coumarin: PVA)/p-Si structures were investigated using C/G-V-f measurements in wide range of frequency (10 kHz–1 MHz) and voltage (± 5 V) by 0.05 V steps. These parameters showed strong dependence on frequency and voltage due to the existence of surface states (N_ss), their life/relaxation time (τ), series resistance (R_s), and polarization processes. ε′ and ε″ values were found to be high at lower frequencies and this was explained by the fact that the interfacial dipoles have enough time to orient themselves in the direction of the signal and thus N_ss can easily follow it. M′−V and M″−V plots both have a distinctive peak at depletion region and peak position shifts toward accumulation region with increasing frequency due to restructuring and reordering of N_ss under electric field and polarization. ln(σ)−ln(f) plots for accumulation region show two linear parts with different slopes, and this provides an evidence to the existence of two different conduction mechanisms which correspond to intermediate and high frequency regions. The strong dispersion in ε′ and ε″ at lower frequencies was attributed to the N_ss, Maxwell–Wagner-type polarizations.