Electric and Dielectric Properties of Au/ZnS-PVA/n-Si (MPS) Structures in the Frequency Range of 10–200 kHz

Abstract

Pure polyvinyl alcohol (PVA) capped ZnS semiconductor nanocrystals were prepared by microwave-assisted method, and the optical and structural properties of the as-prepared materials were characterized by x-ray diffraction (XRD) and Ultraviolet–visible (UV-Vis) techniques. The XRD pattern shows the formation of ZnS nanocrystals, and the UV–Vis spectroscopy results show a blue shift of about 1.2 eV in its band gap due to the confinement of very small nanostructures. The concentration of donor atoms (ND), diffusion potential (VD), Fermi energy level (EF), and barrier height (ΦB (C–V)) values were obtained from the reverse bias C−2–V plots for each frequency. The voltage dependent profile of series resistance (Rs) and surface states (Nss) were also obtained using admittance and low–high frequency methods, respectively. Rs–V and Nss–V plots both have distinctive peaks in the depletion region due to the spatial distribution charge at the surface states. The effect of Rs and interfacial layer on the C–V and G/ω–V characteristics was found remarkable at high frequencies. Therefore, the high frequency C–V and G/ω–V plots were corrected to eliminate the effect of Rs. The real and imaginary parts of dielectric constant (e′ and e″) and electric modulus (M′ and M″), loss tangent (tan δ), and ac electrical conductivity (σac) were also obtained using C and G/ω data and it was found that these parameters are indeed strong functions of frequency and applied bias voltage. Experimental results confirmed that the Nss, Rs , and interfacial layer of the MPS structure are important parameters that strongly influence both the electrical and dielectric properties. The low values of Nss (~109 eV−1 cm−2) and the value of dielectric constant (e′ = 1.3) of ZnS-PVA interfacial layer even at 10 kHz are very suitable for electronic devices when compared with the SiO2. These results confirmed that the ZnS-PVA considerably improves the performance of Au/n-Si (MS) structure and also allow it to work as a capacitor, which stores electric charges or energy.