Investigation of Pulsed Laser Deposited Ni/TiO2/p-Si/Al Heterojunction using Impedance Spectroscopy at Low Temperatures

In this paper, the dielectric characteristics as a function of temperature and frequency for the Ni/TiO2/p-Si/Al heterojunction were studied. The X-ray diffraction studies have proved that deposited films are nanocrystals with particle size of 43.3 nm. The calculated roughness (Rq) of TiO2 film is 2.9 nm. By thermal coating pure aluminum and nickel metals were deposited to make the contacts to p-Si and n-TiO2, respectively. The capacitance and conductance measurements were carried out for the heterojunction in the temperature range from 80 to 300 K and in the frequency range of 10 kHz to 1 MHz. The study shows that the dielectric constant (epsilon'), dielectric loss (epsilon '') and ac conductivity (sigma(ac)) are sensitive to the temperature and frequency. The dielectric constant and dielectric loss increases with temperature and dispersive in nature at low frequencies and becomes independent at high frequencies. The ac conductivity (sigma(ac)) was analyzed by using power law and found to increase with temperature and frequency. The frequency dependence of ac conductivity at different temperatures indicates that the conduction process is thermally activated. We observed two different slopes in the Arrhenius plot for ac conductivity which indicate the presence of two distinct trap states in the measured temperature range. Also, the activation energy found to change significantly with the frequency at higher temperatures.