Formation of ZnO nanopowders by the simple ultrasound-assisted method: Exploring the dielectric and electric properties of the Au/(ZnO-PVA)/n-Si structure

ZnO nanopowders have been prepared by a simple ultrasound-assisted method, and the prepared nanopowders have been utilized for fabrication of Au/(ZnO-PVA)/n-Si structures. Size and morphology of ZnO have been studied by X-ray diffraction and scanning electron microscopy (SEM) techniques. The average nanocrystallite size of ZnO nanopowders was estimated less than 50 nm and the XRD pattern are shown in a hexagonal lattice. Its band gap was obtained from Uv-Visible absorption spectrum as 3.15 eV. Electric and dielectric parameters of MPS structures were analyzed by impedance spectroscopy technique. The measured capacitance and conductance have a strong function of frequency and voltage in depletion and accumulation regions because of the presence of interface states (Nss), series resistance (Rs), interfacial (ZnO-PVA) layer and polarization processes particularly at low frequencies. This is because the Nss and dipoles have enough time to follow external ac signal and can be turned around at low frequencies. The barrier height (ΦB) and depletion layer wides (Wd) increase linearly with increasing frequency. The voltage-dependent profile of Nss extracted from the low-high frequency capacitance process and it has two distinctive peaks due to a particular distribution of interface charges at (ZnO-PVA)/n-Si in the forbidden band-gap of Si. The dielectric constants (ε′) and dielectric loss (ε′′) values increase with decreasing frequency, however the tangent loss (tanδ), real and imaginary components of the electric modulus (M′, M′′) and electrical conductivity (σ) increase with increasing frequency. The increase of σac with increasing frequency was attributed to the increase eddies current that leads to the increase in the energy tanδ. Interestingly, the high value of ε′ (≈30) even at 1 kHz shows that the prepared ZnO-PVA nanocomposite interlayer can capability to the storage more and more charges or energy and so it can be used instead of traditional interfacial insulator layers.