Investigation of Electrical Characteristics in Al/CdS-PVA/p-Si (MPS) Structures Using Impedance Spectroscopy Method

Abstract

The cadmium sulfide (CdS) nanopowders have been prepared by ball-milling method, and CdS-polyvinyl alcohol (PVA) nanocompound in the form of film has been deposited on a p-Si wafer as an interfacial layer by spin-coating method. The impedance characteristics of the fabricated Al/CdS-PVA/p-Si (metal-polymer-semiconductor)-type structures were studied in the frequency and voltage range of 5 kHz–5 MHz and ±1 V, respectively, by considering interface states ( $D_{\mathrm {it}})$ , series resistance ( $R_{s})$ , and interfacial layer effects at 300 K. While the voltage and frequency dependence profiles of $D_{\mathrm {it}}$ were evaluated from the low-high frequency capacitance ( $C_{\mathrm {LF}}$ – $C_{\mathrm {HF}}$ ) and Hill-Coleman methods, $R_{s}$ profiles were evaluated from the Nicollian and Brews method. Doping concentration atoms ( $N_{A})$ and barrier height [ $\Phi _{B}$ (capacitance–voltage ( $C$ – $V$ ))] values were also obtained from the reverse bias $C^{-2}$ versus V plots for each frequency. While $D_{\mathrm {it}}$ and $R_{s}$ values decrease with increasing frequency almost exponentially, $\Phi _{B}$ ( $C$ – $V$ ) increases linearly. Therefore, both the measured capacitance ( $C_{m})$ and conductance ( $G_{m}/\omega $ ) values were corrected to eliminate the $R_{s}$ effect. The experimental results show that $R_{s}$ value is more effective on the impedance measurements at high frequencies in the accumulation region, but $D_{\mathrm {it}}$ is effective at low frequencies in the depletion region.