Effect of film thickness on photodiode and photodetector performance of titanium dioxide (TiO2) prepared via solution assisted spin coating method

In this study, Al/TiO2/p-Si heterostructure device with different thicknesses of inorganic TiO2 interfaces were compared based on the morphological structure of the interfacial layers. The effects of these structural differences on the diode characteristics were also investigated. TiO2 thin films of five different thicknesses were deposited on [100] oriented p-Si by the spin-coating method and designated as T1, T2, T3, T4, and T5 depending on the number of coatings. The TiO2 interface layer thicknesses of the devices were measured to be 29.4 nm, 41.2 nm, 158.8 nm, 261.8 nm, and 390 nm, respectively. The surface roughness was determined using an AFM imaging device. It was found that the RMS values of all the thin films were low, ranging from 0.24 nm to 0.34 nm, regardless of the film thickness, and the surfaces were very smooth. The crystal structure of the TiO2 thin films was investigated by XRD analysis, and lattice parameters were determined by the Scherrer method. It was found that all the films were in the anatase phase. The effect of the structural differences in the TiO2 interfaces on the electrical properties of the devices was investigated using current–voltage measurements in the dark and under different illumination intensities. Basic electrical parameters such as barrier height (ΦB), ideality factor (n), series resistance (Rs), and interfacial density of states (Nss) were calculated from the I-V characteristics using thermionic emission theory and the Norde method. It has been determined that the correction ratios and photodiode and photovoltaic properties of devices with nanosized TiO2 interface layers are stronger both in the dark and at room temperature.