Frequency-resolved electrical characterization and impedance spectroscopy Al/PANI/n-Si heterojunction devices

Hybrid metal–polymer–semiconductor (MPS) diodes based on conducting polymers frequently exhibit inconsistent diode parameters when characterized using a single electrical technique, limiting the physical interpretation of charge transport. In this work, Al/PANI/n-Si heterojunction devices were investigated using a combined frequency-resolved experimental approach supported by numerical modeling. A spin-coated polyaniline (PANI) interlayer of ~ 75 nm thickness was employed, and the devices were characterized at room temperature by current–voltage (I–V), capacitance–voltage (C–V), conductance–voltage (G–V), and impedance spectroscopy measurements over the frequency range of 1 Hz–1 MHz. Thermionic-emission analysis of the I–V data yields an effective ideality factor of n ≈ 2.83 n ≈ 2.83 and a barrier height of φ B≈ 0.67 eV ϕ B ≈ 0.67 e V and a saturation current of I₀≈ 4.5 × 10⁻⁷ A I 0 ≈ 4.5 × 10 - 7 A , indicating pronounced non-ideal transport. Series resistance analysis indicated Rs ≈ 3.2 × 10⁵ Ω R s ≈ 3.2 × 10 5 Ω , consistent with interface-limited conduction. A one-dimensional SCAPS-1D model incorporating experimentally constrained parameters reproduced the rectification and forward-bias behavior, while deviations in reverse leakage current and conductance were attributed to barrier inhomogeneity, trap-assisted transport, and finite contact resistance. Impedance spectroscopy revealed a single dominant relaxation process associated with the depletion capacitance at the PANI/n-Si interface, with capacitance values on the order of 2 × 10- 9 F 2 × 10 - 9 F at 100 kHz, supported by semicircular Nyquist characteristics and equivalent-circuit analysis. These results demonstrate that conventional I–V analysis alone is insufficient to fully describe transport in polymer–Si MPS junctions, and that frequency-resolved characterization—complemented by predictive numerical modeling—provides a reliable framework for understanding and optimizing hybrid optoelectronic devices.