Effect of Annealing on Optical, Electrical and Charge Trapping Properties of TiO₂ NPs Arrays

Glancing angle deposition technique has been carried out to synthesize TiO₂ nanoparticles over SiO(x) thin film. The samples were annealed at different temperatures 550 °C and 950 °C. The average grain sizes and surface RMS roughness have been increased from 9 nm, 0.62 nm (as deposited); 21 nm, 2.47 nm (550 °C annealed) to 37 nm, 4.2 nm (950 °C annealed). Fivefold maximum increase in optical absorption has been recorded for the 950 °C annealed sample as compared to that of the as grown. The absorption and photoluminescence peaks show the red shift with an increase in annealing temperature and grain sizes. Transmission electron microscopy (TEM) has been used to investigate phases of nanoparticles. The junction capacitance of the Au/TiO₂ NPs device was observed to decrease with an increase in frequency. A minimum change in junction capacitance of 1 pF was calculated for 950 °C annealed device for the variation of frequency from 500 Hz to 1 MHz. The results are used to simulate the capacitance as a function of frequency and voltage characteristic of TiO₂ NPs based device in different temperature. Simulated results are exceptionally close to experimental results. The TiO₂ NPs based device annealed at 950 °C possessed higher impedance and lower conductance among all three type of devices. The sample annealed at 950 °C showed the maximum capacitance (0.09 pF at 0 V) as well as charge (˜0.6 Coulomb at +8 V) retention compared to that of the 550 °C annealed and as deposited samples.